Methods of increasing abiotic stress tolerance and/or biomass in plants and plants generated thereby

ABSTRACT

Polynucleotide sequences and methods of utilizing same for increasing the tolerance of a plant to abiotic stresses and/or increasing the biomass and/or increasing the yield of a plant are provided.

RELATED APPLICATIONS

This application is a Continuation-In-Part (CIP) of PCT Patent Application No. PCT/IL2004/000431, filed on May 20, 2004, which claims priority from U.S. Provisional Patent Application No. 60/472,433, filed on May 22, 2003. This application also claims priority from U.S. Provisional Patent Application No. 60/707,957, filed on Aug. 15, 2005. The contents of the above Applications are incoporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to methods of increasing abiotic stress tolerance and/or biomass in plants and, more particularly, to plants expressing exogenous abiotic stress-tolerance genes.

Abiotic stress (also referred to as “environmental stress”) conditions such as salinity, drought, flood, suboptimal temperature and toxic chemical pollution, cause substantial damage to agricultural plants. Most plants have evolved strategies to protect themselves against these conditions. However, if the severity and duration of the stress conditions are too great, the effects on plant development, growth and yield of most crop plants are profound. Furthermore, most crop plants are very susceptible to abiotic stress (ABS) and thus necessitate optimal growth conditions for commercial crop yields. Continuous exposure to stress causes major alterations in plant metabolism which ultimately lead to cell death and consequently yields losses. Thus, despite extensive research and the use of sophisticated and intensive crop-protection measures, losses due to abiotic stress conditions remain in the billions of dollars annually (1,2).

Developing stress-tolerant plants is a strategy that has the potential to solve or mediate at least some of these problems. However, traditional plant breeding strategies used to develop new lines of plants that exhibit tolerance to ABS are relatively inefficient since they are tedious, time consuming and of unpredictable outcome. Furthermore, limited germplasm resources for stress tolerance and incompatibility in crosses between distantly related plant species represent significant problems encountered in conventional breeding. Additionally, the cellular processes leading to ABS tolerance are complex in nature and involve multiple mechanisms of cellular adaptation and numerous metabolic pathways (4-7).

Genetic engineering efforts, aimed at conferring abiotic stress tolerance to transgenic crops, have been described in the prior art. Studies by Apse and Blumwald (Curr Opin Biotechnol. 13:146-150, 2002), Quesada et al. (Plant Physiol. 130:951-963, 2002), Holmström et al. (Nature 379: 683-684, 1996), Xu et al. (Plant Physiol 110: 249-257, 1996), Pilon-Smits and Ebskamp (Plant Physiol 107: 125-130, 1995) and Tarczynski et al. (Science 259: 508-510, 1993) have all attempted at generating stress tolerant plants.

In addition, several U.S. patents and patent applications also describe polynucleotides associated with stress tolerance and their use in generating stress tolerant plants. U.S. Pat. Nos. 5,296,462 and 5,356,816 describe transforming plants with polynucleotides encoding proteins involved in cold adaptation in Arabidopsis thaliana, to thereby promote cold tolerance in the transformed plants.

U.S. Pat. No. 6,670,528 describes transforming plants with polynucleotides encoding polypeptides binding to stress responsive elements, to thereby promote tolerance of the transformed plants to abiotic stress.

U.S. Pat. No. 6,720,477 describes transforming plants with a polynucleotide encoding a signal transduction stress-related protein, capable of increasing tolerance of the transformed plants to abiotic stress.

U.S. application Ser. Nos. 09/938,842 and 10/342,224 describe abiotic stress-related genes and their use to confer upon plants tolerance to abiotic stress.

U.S. application Ser. No. 10/231,035 describes overexpressing a molybdenum cofactor sulfurase in plants to thereby increase their tolerance to abiotic stress.

Although the above described studies were at least partially successful in generating stress tolerant plants, there remains a need for stress tolerant genes which can be utilized to generate plants tolerant of a wide range of abiotic stress conditions.

While reducing the present invention to practice, the present inventors have identified through bioinformatic and laboratory studies several novel abiotic stress-tolerance genes, which can be utilized to increase tolerance to abiotic stress and/or biomass in plants.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a method of increasing tolerance of a plant to an abiotic stress. The method includes expressing within the plant an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252.

According to an additional aspect of the present invention there is provided a method of increasing tolerance of a plant to an abiotic stress. The method includes expressing within the plant an exogenous polynpeptide including an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230.

According to another aspect of the present invention there is provided a method of increasing biomass and/or yield of a plant. The method includes expressing within the plant an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252.

According to still additional aspect of the present invention there is provided a method of increasing biomass and/or yield of a plant. The method includes expressing within the plant an exogenous polypeptide including an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230.

According to yet another aspect of the present invention there is provided a plant cell comprising an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252.

According to yet another aspect of the present invention there is provided a plant cell comprising an exogenous polynucleotide encoding a polypeptide including an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230.

According to still another aspect of the present invention there is provided a nucleic acid construct, including a polynucleotide at least 90% homologous to a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252 and a promoter capable of directing transcription of the polynucleotide in a host cell.

According to another aspect of the present invention there is provided a nucleic acid construct, including a polynucleotide encoding a polypeptide comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230 and a promoter capable of directing transcription of the polynucleotide in a host cell.

According to further yet another aspect of the present invention there is provided an isolated polypeptide, including an amino acid sequence at least 90% homologous to the amino acid sequence encoded by a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252.

According to an additional aspect of the present invention there is provided an isolated polypeptide including an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230.

According to further features in preferred embodiments of the invention described below, the expressing is effected by (i) transforming a cell of the plant with the exogenous polynucleotide; (ii) generating a mature plant from the cell; and (iii) cultivating the mature plant under conditions suitable for expressing the exogenous polynucleotide within the mature plant.

According to still further features in the described preferred embodiments the transforming is effected by introducing to the plant cell a nucleic acid construct including the exogenous polynucleotide and at least one promoter capable of directing transcription of the exogenous polynucleotide in the plant cell.

According to still further features in the described preferred embodiments the at least one promoter is a constitutive promoter.

According to still further features in the described preferred embodiments the constitutive promoter is CaMV 35S promoter.

According to still further features in the described preferred embodiments the constitutive promoter is At6669 promoter.

According to still further features in the described preferred embodiments the at least one promoter is an inducible promoter.

According to still further features in the described preferred embodiments the inducible promoter is an abiotic stress inducible promoter.

According to still further features in the described preferred embodiments the at least one promoter is a tissue-specific promoter.

According to still further features in the described preferred embodiments the expressing is effected by infecting the plant with a virus including the exogenous polynucleotide.

According to still further features in the described preferred embodiments the virus is an avirulent virus.

According to still further features in the described preferred embodiments the abiotic stress is selected from the group consisting of salinity, water deprivation, low temperature, high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, nutrient excess, atmospheric pollution and UV irradiation.

According to still further features in the described preferred embodiments the plant is a dicotyledonous plant.

According to still further features in the described preferred embodiments the plant is a monocotyledonous plant.

According to still further features in the described preferred embodiments the plant cell forms a part of a plant.

The present invention successfully addresses the shortcomings of the presently known configurations by providing methods of utilizing novel abiotic stress-tolerance genes to increase plants tolerance to abiotic stress and/or biomass and/or commercial yield.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

FIG. 1 is a flow chart illustrating a process of identifying putative plant stress-tolerance genes from nucleic-acid sequence databases;

FIG. 2 is a photograph of tomato seedling of a sensitive line (Evoline 1, Evogene, Rehovot, Israel) as seen on the left and a tolerant line (Evoline 2, Evogene, Rehovot, Israel) as seen on the right following 4 week growth under water irrigation containing 300 mM NaCl. Evoline1 was proved for several seasons as being a relatively salt-sensitive line. Evoline 2 was proved for several seasons as being a highly salt-tolerant line;

FIGS. 3A-D are photographs illustrating a T2 transgenic Arabidopsis thaliana mature plant at flowering stage, expressing exogenous luciferase transgene from the At6669 promoter. The same plant is shown in FIGS. 3A and 3B and a second plant is shown in FIGS. 3C and 3D. FIGS. 3A and 3C are photographs taken under normal light conditions and FIGS. 3B and 3D are photographs taken in the dark. Strong illumination indicative of luciferase expression is observed in the flower and root tissues;

FIG. 4 is a bar graph illustrating the mean plant dry weight of transgenic T₂ A. thaliana plants grown under salinity stress conditions (irrigated with 100 mM NaCl solution), as compared with similar plants grown under normal conditions (irrigated with water only). The plants were transformed with putative stress tolerance genes of the present invention (ABST_(—)1, 6, 19, 22, 27, 36, 37) and the effect of the promoters (35S vs. 6669) on biomass was examined;

FIG. 5 illustrates the mean fresh weight of transgenic T₁ A. thaliana plants grown under normal and stress conditions (irrigated with 0 or 100 M NaCl solution, respectively). The plants were transformed with putative stress tolerance genes, or with a luciferase reporter gene (control), positioned under the transcriptional control of the At6669 promoter. Means followed by the same letter are not significantly different according to a one way ANOVA T-Test;

FIG. 6A illustrates the mean fresh weight of T₂ A. thaliana plants grown under normal or stress conditions (irrigated with 0 or 100 M NaCl solution, respectively). The plants were transformed with the putative stress tolerance genes of the present invention, or with luciferase reporter gene (control), positioned under the transcriptional control of the 35S promoter. Means followed by the same letter are not significantly different according to a one way ANOVA T-Test;

FIG. 6B illustrates the mean fresh weight of T₂ A. thaliana plants grown under normal or stress conditions (irrigated with 0 or 100 M NaCl solution, respectively). The plants were transformed with the putative stress tolerance genes of the present invention, or with luciferase reporter gene (control), positioned under the transcriptional control of the At6669 promoter. Means followed by the same letter are not significantly different according to a one way ANOVA T-Test;

FIG. 7 illustrates the total seed weight from T₂ A. thaliana plants over-expressing the ABST genes of the present invention regulated by the 6669 promoter grown under regular conditions. Means followed by the same letter are not significantly different according to a one way ANOVA T-Test;

FIGS. 8A-D are photographs depicting control and transgenic tomato plants (of the genetic background of Evoline3) of the present invention illustrating the increase in yield following over-expression of the putative ABST genes of the present invention. FIG. 8A is a photograph of a tomato plant over-expressing ABST_(—)1, SEQ ID NO. 1 (right; 28) compared to its isogenic line that does not carry the gene (left; 29). FIG. 8B is a photograph of roots from a tomato plant over-expressing ABST_(—)1, SEQ I.D. NO. 1 (right; 28) compared to its isogenic line that does not carry the gene (left; 29). FIG. 8C is a photograph of tomato plant canopies of a plant over-expressing ABST_(—)36, SEQ I.D. NO. 13 (right; 30) compared to a control plant (left; 31). FIG. 8D is a photograph of total fruits of a tomato plant over-expressing ABST_(—)36, SEQ I.D. NO. 13 (right; 30) compared to a control plant (left; 31); and

FIGS. 9A-C are line graphs illustrating the relative expression of putative ABST genes in stress tolerant tomato leaves (Evoline 2) versus stress sensitive tomato leaves (Evoline 1). FIG. 9A illustrates the relative expression of ABST_(—)36 gene in Evoline 2 tomato leaves following salt induction compared to its expression in leaves of the Evoline 1 variety. FIG. 9B illustrates the relative expression of ABST_(—)36 gene in Evoline 2 tomato roots following salt induction compared to its expression in roots of the Evoline 1 variety. FIG. 9C illustrates the relative expression of ABST_(—)37 gene in Evoline 2 tomato leaves following salt induction compared to its expression in leaves of the Evoline 1 variety.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of methods of increasing plants tolerance to abiotic stress and/or biomass by utilizing novel abiotic stress tolerance genes and of plants exhibiting increased tolerance to stress conditions and/or increased capacity to accumulate biomass.

The principles and operation of the present invention may be better understood with reference to the drawings and accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

While reducing the present invention to practice, the present inventors while employing bioinformatic techniques, identified polynucleotide sequences which encode putative abiotic-stress tolerance (ABST) proteins (Examples 1 and 11). Selected sequences were isolated (Examples 3 and 12), cloned into expression vectors (Example 4 and 13) and introduced into Arabidopsis thaliana plants (Example 8) and tomato plants (Example 10). These plants, which were grown under salinity stress conditions, or under normal conditions, exhibited significantly higher biomass as compared with similar plants not carrying the exogenous ABST genes (Examples 9 and 10).

Thus, according to one aspect of the present invention, there is provided a method of increasing tolerance of a plant to an abiotic stress and/or plant biomass. The method includes expressing within the plant an exogenous polynucleotide at least 70% homologous, preferably at least 80% homologous, more preferably at least 85% homologous, most preferably at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252. Alternatively, the exogenous polynucleotide of the present invention encodes a polypeptide having an amino acid sequence selected from the group consisting of SEQ ID NOs: 39-92 and 105-230.

As demonstrated in Example 8 herein below, introduction of SEQ ID NOs: 1, 4, 9, 13 and 14 into Arabidopsis thaliana plants increased plant tolerance to abiotic stress, such as a salinity stress as measured by an increase in fresh weight, dry weight, and/or seed weight. Transgenic tomato plants showed an increase in fresh canopy weight, dry weight, root weight, seed weight and increase in total fruit yield during abiotic stress, such as salinity or drought stress following introduction of these polynucleotide sequences as demonstrated in Example 10.

The nucleic acid sequences of the present invention may be altered, to further improve expression levels for example, by optimizing the nucleic acid sequence in accordance with the preferred codon usage for a particular plant cell type which is selected for the expression of the polypeptides of the present invention.

Construction of synthetic genes by altering the codon usage is described in for example PCT Patent Application WO 93/07278.

Alternatively, ortholog sequences in a particular plant may be identified (e.g. by bioinformatics techniques) as described in Example 10. Following qualification, these may be used to direct the expression of the polypeptides of the present invention in a particular plant species. Since this may increase the probabibilty of gene silencing, it may be preferable to optimize the nucleic acid sequence in accordance with the preferred codon usage as described above.

The phrase “abiotic stress” used herein refers to any adverse effect on metabolism, growth, reproduction and/or viability of a plant. Accordingly, abiotic stress can be induced by suboptimal environmental growth conditions such as, for example, salinity, water deprivation, flooding, low or high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, atmospheric pollution or UV irradiation.

The phrase “abiotic stress tolerance” as used herein refers to the ability of a plant to endure an abiotic stress without suffering a substantial alteration in metabolism, growth, productivity and/or viability.

The polynucleotides of the present invention may enhance abiotic stress tolerance by any mechanism. The polynucleotides may enhance abiotic stress tolerance by encoding for polypeptides which increase the amount of water available to the plant. For example, SEQ ID NO: 13 encodes a polypeptide that enhances symplastic water transport. Alternatively the polynucleotides may enhance abiotic stress tolerance by encoding for polypeptides which are involved in enhancing the expression of other proteins involved in in abiotic stress tolerance. For example, SEQ ID NO: 1 encodes a cytoplasmic ribosomal protein and SEQ ID NO: 14 is a transcription factor.

A suitable plant for use with the method of the present invention can be any monocotyledonous or dicotyledonous plant including, but not limited to, maize, wheat, barely, rye, oat, rice, soybean, peanut, pea, lentil and alfalfa, cotton, rapeseed, canola, pepper, sunflower, potato, tobacco, tomato, eggplant, eucalyptus, a tree, an ornamental plant, a perennial grass and a forage crop.

As used herein, the term “exogenous polynucleotide” refers to a nucleic acid sequence which is not naturally expressed within the plant but which, when introduced into the plant either in a stable or transient manner, produces at least one polypeptide product.

Expressing the exogenous polynucleotide of the present invention within the plant can be effected by transforming one or more cells of the plant with the exogenous polynucleotide, followed by generating a mature plant from the transformed cells and cultivating the mature plant under conditions suitable for expressing the exogenous polynucleotide within the mature plant.

Preferably, the transformation is effected by introducing to the plant cell a nucleic acid construct which includes the exogenous polynucleotide of the present invention and at least one promoter capable of directing transcription of the exogenous polynucleotide in the plant cell. Further details of suitable transformation approaches are provided hereinbelow.

As used herein, the term “promoter” refers to a region of DNA which lies upstream of the transcriptional initiation site of a gene to which RNA polymerase binds to initiate transcription of RNA. The promoter controls where (e.g., which portion of a plant, which organ within an animal, etc.) and/or when (e.g., which stage or condition in the lifetime of an organism) the gene is expressed.

Any suitable promoter sequence can be used by the nucleic acid construct of the present invention. Preferably the promoter is a constitutive promoter, a tissue-specific, or an abiotic stress-inducible promoter.

Suitable constitutive promoters include, for example, CaMV 35S promoter (SEQ ID NO: 19; Odell et al., Nature 313:810-812, 1985); Arabidopsis At6669 promoter (SEQ ID NO: 20); maize Ubi 1 (Christensen et al., Plant Sol. Biol. 18:675-689, 1992); rice actin (McElroy et al., Plant Cell 2:163-171, 1990); pEMU (Last et al., Theor. Appl. Genet. 81:581-588, 1991); and Synthetic Super MAS (Ni et al., The Plant Journal 7: 661-76, 1995). Other constitutive promoters include those in U.S. Pat. Nos. 5,659,026, 5,608,149; 5,608,144; 5,604,121; 5,569,597: 5,466,785; 5,399,680; 5,268,463; and 5,608,142.

Suitable tissue-specific promoters include, but not limited to, leaf-specific promoters such as described, for example, by Yamamoto et al., Plant J. 12:255-265, 1997; Kwon et al., Plant Physiol. 105:357-67, 1994; Yamamoto et al., Plant Cell Physiol. 35:773-778, 1994; Gotor et al., Plant J. 3:509-18, 1993; Orozco et al., Plant Mol. Biol. 23:1129-1138, 1993; and Matsuoka et al., Proc. Natl. Acad. Sci. USA 90:9586-9590, 1993.

Suitable abiotic stress-inducible promoters include, but not limited to, salt-inducible promoters such as RD29A (Yamaguchi-Shinozalei et al., Mol. Gen. Genet. 236:331-340, 1993); drought-inducible promoters such as maize rab17 gene promoter (Pla et. al., Plant Mol. Biol. 21:259-266, 1993), maize rab28 gene promoter (Busk et. al., Plant J. 11: 1285-1295, 1997) and maize Ivr2 gene promoter (Pelleschi et. al., Plant Mol. Biol. 39:373-380, 1999); and heat-inducible promoters such as heat tomato hsp80-promoter from tomato (U.S. Pat. No. 5,187,267).

The nucleic acid construct of the present invention preferably further includes an appropriate selectable marker and/or an origin of replication. Preferably, the nucleic acid construct utilized is a shuttle vector, which can propagate both in E. Coli (wherein the construct comprises an appropriate selectable marker and origin of replication) and be compatible for propagation in cells. The construct according to the present invention can be, for example, a plasmid, a bacmid, a phagemid, a cosmid, a phage, a virus or an artificial chromosome.

The nucleic acid construct of the present invention can be utilized to stably or transiently transform plant cells. In stable transformation, the exogenous polynucleotide of the present invention is integrated into the plant genome and as such it represents a stable and inherited trait. In transient transformation, the exogenous polynucleotide is expressed by the cell transformed but it is not integrated into the genome and as such it represents a transient trait.

There are various methods of introducing foreign genes into both monocotyledonous and dicotyledonous plants (Potrykus, I., Annu. Rev. Plant. Physiol., Plant. Mol. Biol. (1991) 42:205-225; Shimamoto et al., Nature (1989) 338:274-276).

The principle methods of causing stable integration of exogenous DNA into plant genomic DNA include two main approaches:

(i) Agrobacterium-mediated gene transfer: Klee et al. (1987) Annu. Rev. Plant Physiol. 38:467-486; Klee and Rogers in Cell Culture and Somatic Cell Genetics of Plants, Vol. 6, Molecular Biology of Plant Nuclear Genes, eds. Schell, J., and Vasil, L. K., Academic Publishers, San Diego, Calif. (1989) p. 2-25; Gatenby, in Plant Biotechnology, eds. Kung, S. and Arntzen, C. J., Butterworth Publishers, Boston, Mass. (1989) p. 93-112.

(ii) Direct DNA uptake: Paszkowski et al., in Cell Culture and Somatic Cell Genetics of Plants, Vol. 6, Molecular Biology of Plant Nuclear Genes eds. Schell, J., and Vasil, L. K., Academic Publishers, San Diego, Calif. (1989) p. 52-68; including methods for direct uptake of DNA into protoplasts, Toriyama, K. et al. (1988) Bio/Technology 6:1072-1074. DNA uptake induced by brief electric shock of plant cells: Zhang et al. Plant Cell Rep. (1988) 7:379-384. Fromm et al. Nature (1986) 319:791-793. DNA injection into plant cells or tissues by particle bombardment, Klein et al. Bio/Technology (1988) 6:559-563; McCabe et al. Bio/Technology (1988) 6:923-926; Sanford, Physiol. Plant. (1990) 79:206-209; by the use of micropipette systems: Neuhaus et al., Theor. Appl. Genet. (1987) 75:30-36; Neuhaus and Spangenberg, Physiol. Plant. (1990) 79:213-217; glass fibers or silicon carbide whisker transformation of cell cultures, embryos or callus tissue, U.S. Pat. No. 5,464,765 or by the direct incubation of DNA with germinating pollen, DeWet et al. in Experimental Manipulation of Ovule Tissue, eds. Chapman, G. P. and Mantell, S. H. and Daniels, W. Longman, London, (1985) p. 197-209; and Ohta, Proc. Natl. Acad. Sci. USA (1986) 83:715-719.

The Agrobacterium system includes the use of plasmid vectors that contain defined DNA segments that integrate into the plant genomic DNA. Methods of inoculation of the plant tissue vary depending upon the plant species and the Agrobacterium delivery system. A widely used approach is the leaf disc procedure which can be performed with any tissue explant that provides a good source for initiation of whole plant differentiation. Horsch et al. in Plant Molecular Biology Manual A5, Kluwer Academic Publishers, Dordrecht (1988) p. 1-9. A supplementary approach employs the Agrobacterium delivery system in combination with vacuum infiltration. The Agrobacterium system is especially viable in the creation of transgenic dicotyledonous plants.

There are various methods of direct DNA transfer into plant cells. In electroporation, the protoplasts are briefly exposed to a strong electric field. In microinjection, the DNA is mechanically injected directly into the cells using very small micropipettes. In microparticle bombardment, the DNA is adsorbed on microprojectiles such as magnesium sulfate crystals or tungsten particles, and the microprojectiles are physically accelerated into cells or plant tissues.

Following stable transformation plant propagation is exercised. The most common method of plant propagation is by seed. Regeneration by seed propagation, however, has the deficiency that due to heterozygosity there is a lack of uniformity in the crop, since seeds are produced by plants according to the genetic variances governed by Mendelian rules. Basically, each seed is genetically different and each will grow with its own specific traits. Therefore, it is preferred that the transformed plant be produced such that the regenerated plant has the identical traits and characteristics of the parent transgenic plant. Therefore, it is preferred that the transformed plant be regenerated by micropropagation which provides a rapid, consistent reproduction of the transformed plants.

Micropropagation is a process of growing new generation plants from a single piece of tissue that has been excised from a selected parent plant or cultivar. This process permits the mass reproduction of plants having the preferred tissue expressing the fusion protein. The new generation plants which are produced are genetically identical to, and have all of the characteristics of, the original plant. Micropropagation allows mass production of quality plant material in a short period of time and offers a rapid multiplication of selected cultivars in the preservation of the characteristics of the original transgenic or transformed plant. The advantages of cloning plants are the speed of plant multiplication and the quality and uniformity of plants produced.

Micropropagation is a multi-stage procedure that requires alteration of culture medium or growth conditions between stages. Thus, the micropropagation process involves four basic stages: Stage one, initial tissue culturing; stage two, tissue culture multiplication; stage three, differentiation and plant formation; and stage four, greenhouse culturing and hardening. During stage one, initial tissue culturing, the tissue culture is established and certified contaminant-free. During stage two, the initial tissue culture is multiplied until a sufficient number of tissue samples are produced to meet production goals. During stage three, the tissue samples grown in stage two are divided and grown into individual plantlets. At stage four, the transformed plantlets are transferred to a greenhouse for hardening where the plants' tolerance to light is gradually increased so that it can be grown in the natural environment.

Preferably, mature transformed plants generated as described above are further selected for abiotic stress tolerance. Accordingly, transformed and non-transformed (wild type) plants are exposed to an abiotic stress condition, such as water depravation, suboptimal temperature, nutrient deficiency, or preferably a salt stress condition. Salt stress can be effected in many ways such as, for example, by irrigating the plants with a hyperosmotic solution, by cultivating the plants hydroponically in a hyperosmotic growth solution (e.g., Hoagland solution), or by culturing the plants in a hyperosmotic growth medium (e.g., MS medium). Since different plants vary considerably in their tolerance to salinity, the salt concentration in the irrigation water, growth solution, or growth medium is preferably adjusted according to the specific characteristics of the specific plant cultivar or variety, so as to inflict a mild or moderate effect on the physiology and/or morphology of the plants (for guidelines as to appropriate concentration see, Bernstein and Kafkafi, Root Growth Under Salinity Stress In: Plant Roots, The Hidden Half 3rd ed. Waisel Y, Eshel A and Kafkafi U. (editors) Marcel Dekker Inc., New York, 2002, and reference therein). Following exposure to the stress condition the plants are frequently monitored until substantial physiological and/or morphological effects appear in wild type plants. Subsequently, transformed plants not exhibiting substantial physiological and/or morphological effects, or exhibiting higher biomass than wild-type plants, are identified as abiotic stress tolerant plants.

Although stable transformation is presently preferred, transient transformation of leaf cells, meristematic cells or the whole plant is also envisaged by the present invention.

Transient transformation can be effected by any of the direct DNA transfer methods described above or by viral infection using modified plant viruses.

Viruses that have been shown to be useful for the transformation of plant hosts include CaMV, TMV and BV. Transformation of plants using plant viruses is described in U.S. Pat. No. 4,855,237 (BGV), EP-A 67,553 (TMV), Japanese Published Application No. 63-14693 (TMV), EPA 194,809 (BV), EPA 278,667 (BV); and Gluzman, Y. et al., Communications in Molecular Biology: Viral Vectors, Cold Spring Harbor Laboratory, New York, pp. 172-189 (1988). Pseudovirus particles for use in expressing foreign DNA in many hosts, including plants, is described in WO 87/06261.

Preferably, the virus of the present invention is avirulent and thus is incapable of causing severe symptoms such as reduced growth rate, mosaic, ring spots, leaf roll, yellowing, streaking, pox formation, tumor formation and pitting. A suitable avirulent virus may be a naturally occurring avirulent virus or an artificially attenuated virus. Virus attenuation may be effected by using methods well known in the art including, but not limited to, sub-lethal heating, chemical treatment or by directed mutagenesis techniques such as described, for example, by Kurihara and Watanabe (Molecular Plant Pathology 4:259-269, 2003), Gal-on et al. (1992), Atreya et al. (1992) and Huet et al. (1994).

Suitable virus strains can be obtained from available sources such as, for example, the American Type culture Collection (ATCC) or by isolation from infected plants. Isolation of viruses from infected plant tissues can be effected by techniques well known in the art such as described, for example by Foster and Tatlor, Eds. “Plant Virology Protocols: From Virus Isolation to Transgenic Resistance (Methods in Molecular Biology (Humana Pr), Vol 81)”, Humana Press, 1998. Briefly, tissues of an infected plant believed to contain a high concentration of a suitable virus, preferably young leaves and flower petals, are ground in a buffer solution (e.g., phosphate buffer solution) to produce a virus infected sap which can be used in subsequent inoculations.

Construction of plant RNA viruses for the introduction and expression of non-viral exogenous polynucleotide sequences in plants is demonstrated by the above references as well as by Dawson, W. O. et al., Virology (1989) 172:285-292; Takamatsu et al. EMBO J. (1987) 6:307-311; French et al. Science (1986) 231:1294-1297; and Takamatsu et al. FEBS Letters (1990) 269:73-76.

When the virus is a DNA virus, suitable modifications can be made to the virus itself. Alternatively, the virus can first be cloned into a bacterial plasmid for ease of constructing the desired viral vector with the foreign DNA. The virus can then be excised from the plasmid. If the virus is a DNA virus, a bacterial origin of replication can be attached to the viral DNA, which is then replicated by the bacteria. Transcription and translation of this DNA will produce the coat protein which will encapsidate the viral DNA. If the virus is an RNA virus, the virus is generally cloned as a cDNA and inserted into a plasmid. The plasmid is then used to make all of the constructions. The RNA virus is then produced by transcribing the viral sequence of the plasmid and translation of the viral genes to produce the coat protein(s) which encapsidate the viral RNA.

Construction of plant RNA viruses for the introduction and expression in plants of non-viral exogenous polynucleotide sequences such as those included in the construct of the present invention is demonstrated by the above references as well as in U.S. Pat. No. 5,316,931.

In one embodiment, a plant viral polynucleotide is provided in which the native coat protein coding sequence has been deleted from a viral polynucleotide, a non-native plant viral coat protein coding sequence and a non-native promoter, preferably the subgenomic promoter of the non-native coat protein coding sequence, capable of expression in the plant host, packaging of the recombinant plant viral polynucleotide, and ensuring a systemic infection of the host by the recombinant plant viral polynucleotide, has been inserted. Alternatively, the coat protein gene may be inactivated by insertion of the non-native polynucleotide sequence within it, such that a protein is produced. The recombinant plant viral polynucleotide may contain one or more additional non-native subgenomic promoters. Each non-native subgenomic promoter is capable of transcribing or expressing adjacent genes or polynucleotide sequences in the plant host and incapable of recombination with each other and with native subgenomic promoters. Non-native (foreign) polynucleotide sequences may be inserted adjacent the native plant viral subgenomic promoter or the native and a non-native plant viral subgenomic promoters if more than one polynucleotide sequence is included. The non-native polynucleotide sequences are transcribed or expressed in the host plant under control of the subgenomic promoter to produce the desired products.

In a second embodiment, a recombinant plant viral polynucleotide is provided as in the first embodiment except that the native coat protein coding sequence is placed adjacent one of the non-native coat protein subgenomic promoters instead of a non-native coat protein coding sequence.

In a third embodiment, a recombinant plant viral polynucleotide is provided in which the native coat protein gene is adjacent its subgenomic promoter and one or more non-native subgenomic promoters have been inserted into the viral polynucleotide. The inserted non-native subgenomic promoters are capable of transcribing or expressing adjacent genes in a plant host and are incapable of recombination with each other and with native subgenomic promoters. Non-native polynucleotide sequences may be inserted adjacent the non-native subgenomic plant viral promoters such that the sequences are transcribed or expressed in the host plant under control of the subgenomic promoters to produce the desired product.

In a fourth embodiment, a recombinant plant viral polynucleotide is provided as in the third embodiment except that the native coat protein coding sequence is replaced by a non-native coat protein coding sequence.

The viral vectors are encapsidated by the coat proteins encoded by the recombinant plant viral polynucleotide to produce a recombinant plant virus. The recombinant plant viral polynucleotide or recombinant plant virus is used to infect appropriate host plants. The recombinant plant viral polynucleotide is capable of replication in the host, systemic spread in the host, and transcription or expression of foreign gene(s) (exogenous polynucleotide) in the host to produce the desired protein.

Techniques for inoculation of viruses to plants may be found in Foster and Taylor, eds. “Plant Virology Protocols: From Virus Isolation to Transgenic Resistance (Methods in Molecular Biology (Humana Pr), Vol 81)”, Humana Press, 1998; Maramorosh and Koprowski, eds. “Methods in Virology” 7 vols, Academic Press, New York 1967-1984; Hill, S. A. “Methods in Plant Virology”, Blackwell, Oxford, 1984; Walkey, D. G. A. “Applied Plant Virology”, Wiley, New York, 1985; and Kado and Agrawa, eds. “Principles and Techniques in Plant Virology”, Van Nostrand-Reinhold, New York.

In addition to the above, the polynucleotide of the present invention can also be introduced into a chloroplast genome thereby enabling chloroplast expression.

A technique for introducing exogenous polynucleotide sequences to the genome of the chloroplasts is known. This technique involves the following procedures. First, plant cells are chemically treated so as to reduce the number of chloroplasts per cell to about one. Then, the exogenous polynucleotide is introduced via particle bombardment into the cells with the aim of introducing at least one exogenous polynucleotide molecule into the chloroplasts. The exogenous polynucleotides selected such that it is integratable into the chloroplast's genome via homologous recombination which is readily effected by enzymes inherent to the chloroplast. To this end, the exogenous polynucleotide includes, in addition to a gene of interest, at least one polynucleotide stretch which is derived from the chloroplast's genome. In addition, the exogenous polynucleotide includes a selectable marker, which serves by sequential selection procedures to ascertain that all or substantially all of the copies of the chloroplast genomes following such selection will include the exogenous polynucleotide. Further details relating to this technique are found in U.S. Pat. Nos. 4,945,050; and 5,693,507 which are incorporated herein by reference. A polypeptide can thus be produced by the protein expression system of the chloroplast and become integrated into the chloroplast's inner membrane.

Since abiotic stress tolerance in plants can involve multiple genes acting additively or in synergy (see, for example, in Quesda et al., Plant Physiol. 130:951-063, 2002), the present invention also envisages expressing a plurality of exogenous polynucleotides in a single host plant to thereby achieve superior abiotic stress tolerance.

Expressing a plurality of exogenous polynucleotides in a single host plant can be effected by co-introducing multiple nucleic acid constructs, each including a different exogenous polynucleotide, into a single plant cell. The transformed cell can than be regenerated into a mature plant using the methods described hereinabove.

Alternatively, expressing a plurality of exogenous polynucleotides in a single host plant can be effected by co-introducing into a single plant-cell a single nucleic-acid construct including a plurality of different exogenous polynucleotides. Such a construct can be designed with a single promoter sequence which can transcribe a polycistronic message including all the different exogenous polynucleotide sequences. To enable co-translation of the different polypeptides encoded by the polycistronic message, the polynucleotide sequences can be inter-linked via an internal ribosome entry site (IRES) sequence which facilitates translation of polynucleotide sequences positioned downstream of the IRES sequence. In this case, a transcribed polycistronic RNA molecule encoding the different polypeptides described above will be translated from both the capped 5′ end and the two internal IRES sequences of the polycistronic RNA molecule to thereby produce in the cell all different polypeptides. Alternatively, the construct can include several promoter sequences each linked to a different exogenous polynucleotide sequence.

The plant cell transformed with the construct including a plurality of different exogenous polynucleotides, can be regenerated into a mature plant, using the methods described hereinabove.

Alternatively, expressing a plurality of exogenous polynucleotides in a single host plant can be effected by introducing different nucleic acid constructs, including different exogenous polynucleotides, into a plurality of plants. The regenerated transformed plants can then be cross-bred and resultant progeny selected for superior abiotic stress tolerance and/or biomass traits, using conventional plant breeding techniques.

Hence, the present application provides methods of utilizing novel abiotic stress-tolerance genes to increase tolerance to abiotic stress and/or biomass and/or yield in a wide range of economical plants, safely and cost effectively.

Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non limiting fashion.

Generally, the nomenclature used herein and the laboratory procedures utilized in the present invention include molecular, biochemical, microbiological and recombinant DNA techniques. Such techniques are thoroughly explained in the literature. See, for example, “Molecular Cloning: A laboratory Manual” Sambrook et al., (1989); “Current Protocols in Molecular Biology” Volumes I-III Ausubel, R. M., ed. (1994); Ausubel et al., “Current Protocols in Molecular Biology”, John Wiley and Sons, Baltimore, Md. (1989); Perbal, “A Practical Guide to Molecular Cloning”, John Wiley & Sons, New York (1988); Watson et al., “Recombinant DNA”, Scientific American Books, New York; Birren et al. (eds) “Genome Analysis: A Laboratory Manual Series”, Vols. 1-4, Cold Spring Harbor Laboratory Press, New York (1998); methodologies as set forth in U.S. Pat. Nos. 4,666,828; 4,683,202; 4,801,531; 5,192,659 and 5,272,057; “Cell Biology: A Laboratory Handbook”, Volumes I-III Cellis, J. E., ed. (1994); “Current Protocols in Immunology” Volumes I-III Coligan J. E., ed. (1994); Stites et al. (eds), “Basic and Clinical Immunology” (8th Edition), Appleton & Lange, Norwalk, Conn. (1994); Mishell and Shiigi (eds), “Selected Methods in Cellular Immunology”, W. H. Freeman and Co., New York (1980); available immunoassays are extensively described in the patent and scientific literature, see, for example, U.S. Pat. Nos. 3,791,932; 3,839,153; 3,850,752; 3,850,578; 3,853,987; 3,867,517; 3,879,262; 3,901,654; 3,935,074; 3,984,533; 3,996,345; 4,034,074; 4,098,876; 4,879,219; 5,011,771 and 5,281,521; “Oligonucleotide Synthesis” Gait, M. J., ed. (1984); “Nucleic Acid Hybridization” Hames, B. D., and Higgins S. J., eds. (1985); “Transcription and Translation” Hames, B. D., and Higgins S. J., eds. (1984); “Animal Cell Culture” Freshney, R. I., ed. (1986); “Immobilized Cells and Enzymes” IRL Press, (1986); “A Practical Guide to Molecular Cloning” Perbal, B., (1984) and “Methods in Enzymology” Vol. 1-317, Academic Press; “PCR Protocols: A Guide To Methods And Applications”, Academic Press, San Diego, Calif. (1990); Marshak et al., “Strategies for Protein Purification and Characterization—A Laboratory Course Manual” CSHL Press (1996); all of which are incorporated by reference as if fully set forth herein. Other general references are provided throughout this document. The procedures therein are believed to be well known in the art and are provided for the convenience of the reader.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below.

Example 1 Identifying Putative Abiotic Stress Tolerance Genes

Putative abiotic stress-tolerance (ABST) genes were selected from NCBI databases of tomato expressed sequence tags (ESTs) and cDNAs. The database sequences were clustered and assembled using the LEADS™ software (Compugen). Clustering resulted in more than 20,000 clusters, each representing a different gene. An expression profile summary was compiled for each cluster by pooling all keywords included in the sequence records comprising the cluster. The clusters were then screened to include polynucleotides originating from libraries identified by keywords relating to ABST. The selected clusters were further filtered to exclude any cluster which included more than 100 ESTs per cluster and/or any cluster in which less than 50% of the sequences were annotated by ABST-related keywords.

Prior art ABST plant genes were identified from the publications of Quesada et al. (Plant Physiol. 130:951-963, 2002); Apse and Blumwald (Curr Opin Biotechnol. 13:146-150, 2002); Rontein et al. (Metab Eng 4:49-56, 2002); and references therein. Known plant ABST genes were aligned with the clustered tomato nucleic-acid sequences using the BLAST program. The tomato sequences having an e-score value lower than 5 were identified as ABST orthologes. Additional prior art tomato ABST genes were identified by searching the clustered tomato sequence records using the keywords “root”, “crown gall”, “nutrient”, “callus”, “disease”, “pathogen”, “elicitor” and “pseudomonas”.

Finally, all identified prior art ABST genes were matched (by sequence alignment using the BLAST software) with the output set of tomato gene clusters, selected as described above. Consequently, about 40% of the genes selected in the output set of clusters which matched with prior art ABST genes proved to be known ABST genes, indicating that the remaining genes of the selected clusters are potentially capable of increasing abiotic stress tolerance in plants.

The selected polynucleotide sequences (Table 1A), were analyzed for presence of ORFs using Vector NTI suite (InforMax, U.K.) version 6 (Hasting Software, Inc: www.generunner.com/). ORFs identified in each of these polynucleotide sequences were compared to Genbank database sequences, using Blast (www.ncbi.nlm.nih.gov/BLAST/); the ORF displaying the highest homology to a GenBank sequence or sequences, was mapped in order to identify an ATG start codon. The position of the ATG start codon of this ORF was then compared with that of the identified polynucleotide sequence in order to verify that each of the eighteen sequences described herein includes a full length ORF and an ATG start codon (thus qualifying as a “putative ABST gene”). TABLE 1A Putative ABST genes ABST No. SEQ ID No.  1 1  3 2  5 3  6 4 10 5 11 6 12 7 19 8 22 9 24 10 26 11 27 12 36 13 37 14 39_T0 15 39_T1 16 49_T0 17 49_T1 18

ABST polypeptide homologues were identified from the NCBI databases using BLAST software (Table 1B). TABLE 1B ABST homologues ABST Putative ABST Polypeptide ABST Polypeptide Gene SEQ Homologue Homologue Protein ID No. NCBI Accession No. SEQ ID No. Homology (%) 1 BAA96366 39 98 1 AAS47510 40 98 1 NP_567151 41 97 1 NP_567104 42 96 1 AAK55664 43 96 1 P46298 44 97 1 T01338 45 96 1 T47888 46 95 1 BAD09465 47 92 1 Q05761 48 91 1 BAD09464 49 88 1 CAA79496 50 84 1 EAJ94592 51 85 4 NP_188036 52 76 4 NP_035977 53 70 4 XP_342608 54 69 4 T09295 55 60 4 NP_564717 56 59 4 AAM63624 57 59 9 P37707 58 93 9 CAD37200 59 81 9 CAA04664 60 78 9 AAM64572 61 77 9 NP_189345 62 77 9 NP_974979 63 60 13 AAC49992 64 88 13 T10804 65 87 13 AAL38357 66 87 13 NP_188245 67 87 13 NP_193465 68 87 13 AAG44945 69 86 13 T07819 70 86 13 T12632 71 86 13 CAC39073 72 86 13 T01648 73 86 13 AAF90121 74 86 13 S48116 75 86 13 AAO86710 76 86 13 T14002 77 85 13 T14001 78 85 13 T48886 79 85 13 T14314 80 85 13 P33560 81 85 13 P21653 82 85 13 T14000 83 85 13 T48884 84 85 13 P24422 85 85 13 AAB53329 86 85 14 NP_200279 87 67 14 AAM64276 88 67 14 AAO72577 89 66 14 NP_175518 90 64 14 BAC78588 91 64 14 BAD03011 92 62

Five of these genes were selected as having the most potential of being putative ABS tolerance genes on the basis of digital expression profiles (i.e. known to be up-regulated under different stress conditions) as listed in Tables 2-6, and homologies to public protein sequences and domains through multi sequence alignment searches. Also, only genes with low and medium expression levels were included.

The five genes are listed together with their functions in Table 1C below. TABLE 1C Selected Putative ABST genes Gene Length of Protein Protein domain name AC number, CDS bps length aa Similarities Go classification ABST_1 BG123819/ 833 151 Ribosomal RNA binding, SEQ ID TC153989 protein S13 morphogenesis, protein NO: 1 biosynthesis in cytosol ABST_6 BG627487/ 1242 163 DnaJ domain Chaperone activity, SEQ ID TC162949 protein folding NO: 4 ABST_22 BG127611/ 1518 311 Asparagine-rich Unknown SEQ ID TC154372 region profile NO: 9 ABST_36 AA824892/ 1466 249 Major intrinsic Water channel, SEQ ID TC154006 protein endomembrane activity NO: 13 ABST_37 AW220029/ 1245 244 Helix-loop-helix DNA binding, SEQ ID TC156100 DNA-binding transcription NO: 14 domain factor activity

Digital expression, also known as electronic northern blot, is a tool for virtually displaying the expression profile of query genes based on the EST sequences forming the cluster. The tool can provide the expression profile of a cluster in terms of plant anatomy (in what tissues/organs is the gene expressed), developmental stage (the developmental stages at which a gene can be found) and profile of treatment (provides the physiological conditions under which a gene is expressed such as drought, cold, pathogen infection, etc). Given a random distribution of ESTs in the different clusters, the digital expression provides a probability value that describes the probability of a cluster having a total of N ESTs to contain X ESTs from a certain collection of libraries. For the probability calculations, various considerations are taken: a) the number of ESTs in the cluster, b) the number of ESTs of the implicated and related libraries, c) the overall number of ESTs available representing the species. Thereby clusters with low probability values are highly enriched with ESTs from the group of libraries of interest indicating a specialized expression.

The digital expression profile for ABST_(—)1 (SEQ ID NO: 1) is summarized below in Table 2. TABLE 2 Change in expression of ABST_1 due to exposure to various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value hormone 3 23195 7.14655 0.419783 0.978926 treatment Elicitors and 1 14540 4.47988 0.22322 0.990341 pathogens mix Mix of 2 8655 2.66667 0.749999 0.751616 elicitors nutrient 1 3258 1.00381 0.9962 0.636393 deficiencies —N, —P, —K, 1 3258 1.00381 0.9962 0.636393 —Fe, —Al pathogen 13 30639 9.4401 1.3771 0.141666 Agrobacterium 4 5107 1.5735 2.5421 0.0728454 tumefaciens C58 CONTROL 1 419 1 1 0.12124 Ralstonia s. Elicitors and 1 14540 4.47988 0.22322 0.990341 pathogens mix

The digital expression profile for ABST_(—)6 (SEQ ID NO:4) is summarized below in Table 3. TABLE 3 Change in expression of ABST_6 due to exposure to various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value hormone 3 23195 2.59875 1.1544 0.489866 treatment Mix of 3 8655 1 3 0.0509528 elicitors pathogen 2 30639 3.43276 0.582621 0.876812 pseudomonas 2 10177 1.14022 1.75405 0.316866 syringae

The digital expression profile for ABST_(—)22 (SEQ ID NO:9) is summarized below in Table 4. TABLE 4 Change in expression of ABST_22 due to exposure to various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value hormone 2 23195 5.7389 0.348499 0.982893 treatment Mix of 2 8655 2.14142 0.933961 0.636873 elicitors nutrient 3 3258 1 3 0.0469483 deficiencies —N, —P, —K, 3 3258 1 3 0.0469483 —Fe, —Al pathogen 6 30639 7.58069 0.791485 0.788347 Agrobacterium 2 5107 1.26357 1.58282 0.361357 tumefaciens C58

The digital expression profile for ABST_(—)36 (SEQ ID NO: 13) is summarized below in Table 5. TABLE 5 Change in expression of ABST_36 due to exposure to various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value heavy metals 1 741 1 1 0.307469 0.2 mM CdCl2 1 476 1 1 0.210111 hormone 12 23195 11.4778 1.0455 0.480794 treatment Elicitors and 4 14540 7.19496 0.555945 0.934556 pathogens mix Mix of 8 8655 4.28283 1.86792 0.0656842 elicitors nutrient 9 3258 1.61219 5.58248 3.76416E−05 deficiencies —N, —P, —K, —Fe, 9 3258 1.61219 5.58248 3.76416E−05 —Al pathogen 17 30639 15.1614 1.12127 0.344706 Agrobacterium 3 5107 2.52714 1.18711 0.464783 tumefaciens C58 Elicitors and 4 14540 7.19496 0.555945 0.934556 pathogens mix pseudomonas 10 10177 5.03598 1.98571 0.0295878 syringae

The digital expression profile for ABST_(—)37 (SEQ ID NO: 14) is summarized below in Table 6. TABLE 6 Change in expression of ABST_37 due to exposure to various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value hormone 1 23195 1 1 0.643514 treatment Mix of 1 8655 1 1 0.31009 elicitors nutrient 3 3258 1 3 0.000275679 deficiencies —N, —P, —K, 3 3258 1 3 0.000275679 —Fe, —Al

Example 2 In-Situ Validation/Expression Studies

The five genes listed in Table 1C were validated in situ as putative ABST genes by analyzing their expression profile in tomato plants under favorable, salt and drought stress conditions.

The expression studies were carried out on three tomato lines—sensitive tomato variety (Evoline 1), processing tomato line with moderate tolerance to salt (Evoline 3, also referred to herein as M82) and drought and high salt tolerant tomato line (Evoline 2). All lines were tested for several seasons for their levels of tolerance to salt and other soil stresses such as drought. All lines are commercially available from Evogene, Rehovot, Israel.

Methods

Salt induction: Salt stress induction was performed by introducing the roots of 14 days old tomato seedlings, of different tomato homozygote varieties, into a water bath which contained a solution of Hogland (comprising KNO₃-8 mM, MgSO₄-1 mM, KH₂PO₄-1 mM, and microelements, all dissolved in water, at pH 6.5), and 300 mM NaCl. Plants were placed on a floating tray, such that only the roots were dipped in the solution. Plants were grown in salt solution for 5 weeks during which the degree of tolerance to the salt stress was measured, by comparing plant development and biomass. The experiment was performed in 3 sequential seasons and with 5 repeats for each line in each experiment. The experiments identified 3 tomato lines showing consistent level of either weak (Evoline1), moderate (Evoline3), or high (Evoline2) level of tolerance. During the last experiment RNA samples from leaves and roots from Evoline1 and Evoline3 were taken 5, 9, 72, 240 hours after introducing the plants to salt solution.

Drought induction: Levels of tolerance to drought induction were tested on Evoline1, Evoline2, and Evoline3 tomato plants. The plants were grown in CYG Germination Pouches, (Mega International, MN, USA), from germination until 4 true leaf stage in a regular nutrient solution. Drought conditions were applied by adding polyethylene glycol-PEG to the growth solution to a final concentration of 15%. RNA samples from leaves and roots were taken at time 0, 0.5 h, 3 h, 6 h and 48 h following drought induction. RNA expression level was measured by using quantitative RT PCR.

Results

As illustrated in FIG. 2, seedlings of the sensitive line (Evoline 1) were much smaller with far fewer leaves than seedlings of the tolerant line (Evoline 2) following four weeks growth under water irrigation containing 300 mM NaCl.

Tables 7-9 below summarise the up-regulationchange in gene expression in response to various stress conditions (e.g. drought and salt) of polynucleotides of the present invention in tomato plants as calculated by quantitative RT-PCR. TABLE 7 Relative expression of the ABST genes following salt induction compared to their expression at time 0 (T0) in leaves and roots of a tomato tolerant line (Evoline 2 = highly tolerant line) Time after induction (hours) Organ ABST_1 ABST_6 ABST_19 ABST_22 ABST_27 ABST_36 ABST_37 0 leaves 1.00 1.00 1.00 1.00 1.00 1.00 1.00 5 leaves 1.32 0.56 1.19 1.33 1.61 1.97 1.63 9 leaves 1.54 0.48 0.99 1.51 1.50 1.17 1.76 72 leaves 1.26 0.30 1.13 1.75 1.22 0.57 3.60 240 leaves 0.54 1.89 1.22 0.62 0.46 0.74 8.05 0 roots 1.00 1.00 1.00 1.00 1.00 1.00 1.00 5 roots 0.89 1.23 0.89 1.09 0.66 0.57 1.20 9 roots 0.72 1.03 1.01 0.78 0.69 0.42 0.83 72 roots 0.81 2.06 1.24 1.38 0.97 0.29 1.15 240 roots 0.50 7.91 1.70 0.66 0.57 0.10 4.77

TABLE 8 Relative expression of the ABST genes following salt induction compared to their expression in leaves and roots of tomato sensitive variety (Evoline 1 = salt sensitive line) Time after induction (hours) Organ ABST_1 ABST_6 ABST_19 ABST_22 ABST_27 ABST_36 ABST_37 0 leaves 1.00 1.00 1.00 1.00 1.00 1.00 1.00 5 leaves 1.60 0.00 1.10 1.18 1.58 1.18 0.00 9 leaves 0.88 0.34 1.14 0.83 1.80 0.58 0.83 72 leaves 0.70 0.20 1.21 0.81 0.95 0.40 1.71 240 leaves 0.44 2.25 1.56 0.69 0.56 0.23 7.63 0 roots 1.00 1.00 1.00 1.00 1.00 1.00 1.00 5 roots 0.96 1.56 1.05 1.01 1.25 0.84 0.81 9 roots 0.84 1.10 1.08 0.58 1.09 0.46 0.47 72 roots 0.83 1.31 1.43 1.00 1.41 0.24 0.44 240 roots 0.59 9.13 2.03 0.77 1.00 0.07 1.77

TABLE 9 Relative expression of the ABST genes following drought induction compared to their expression in T0 in leaves and roots of seedlings of processing tomato variety (Evoline 3 = moderate salt tolerant line-M82) Time after induction (h) Organ ABST_1 ABST_6 ABST_19 ABST_22 ABST_27 ABST_36 ABST_37 0 Roots 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.5 Roots 0.62 0.24 0.94 0.58 0.81 0.40 0.51 3 Roots 0.40 0.21 0.77 0.40 0.54 0.25 0.26 6 Roots 0.58 0.13 1.15 0.36 0.82 0.24 0.29 48 Roots 0.72 0.15 1.19 1.43 3.05 0.49 1.30 0 Leaves 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.5 Leaves 2.21 2.84 0.86 2.49 1.37 1.18 0.75 3 Leaves 2.24 3.83 1.40 2.97 0.84 2.55 0.81 6 Leaves 3.29 4.99 1.68 6.47 6.18 2.08 1.91 48 Leaves 2.70 4.99 1.20 8.80 3.60 0.46 1.88

As seen from tables 7-9, ABST 1, 6, 22, 27, 36 and 37 all showed induction of expression under different stress conditions. The changes in gene expression as a response to various stresses could be classified into two main categories—immediate up-regulation e.g. ABST_(—)36 and ABST_(—)1 (from 30 minutes to 6 hours following induction) and delayed up-regulation e.g. ABST_(—)37 and ABST_(—)6 (24 to 240 hours following induction).

The expression profile of most the genes was also affected by the genotype of the plants (highly tolerant line vs. sensitive line) and the specific stress the plants were exposed to (i.e. salt or PEG). Three genes showed changes in expression in leaves only (ABST_(—)1, 22, 36). Only ABST 6 and 37 showed up-regulation of expression in both leaves and roots.

Significant changes were not detected in the expression of the ABST_(—)19 as a response to salt or drought stress.

Table 10 below summarises the main expression modes of the ABST genes of the present invention under salt and osmotic stress. TABLE 10 Expression modes of the ABST genes of the present invention under salt and osmotic stresses Salt stress Osmotic Salt stress Osmotic stress Gene name/ (100 mM NaCl) stress (100 mM Nacl) (10% PEG) time range Evoline 1 Evoline 2 Evoline 3 Evoline 1 Evoline 2 Evoline 3 Leaf Root ABST_1 Up × 1.5 Up × 1.5 Up × 3 Stable Stable Down × 2 Early response ABST_1 Down × 2 Down × 2 Stable Down × 2 Down × 2 Stable Early response ABST_6 Down × 3 Down × 2 Up × 5 Stable Stable Down × 7 Early response ABST_6 Up × 2 Up × 2 Up × 5 Up × 9 Up × 8 Down × 7 Late response ABST_22 Stable Up × 1.5 Up × 6 Stable Stable Down × 3 Early response ABST_22 Stable Stable Up × 8 Stable Stable Stable Late response ABST_36 Stable Up × 2 Up × 2 Down × 2 Down × 2 Down × 5 Early response ABST_36 Down × 5 Stable Down × 2 Down × 5 Down × 3 Down × 2 Late response ABST_37 Stable Up × 2 Stable Down × 2 Stable Down × 3 Early response ABST_37 Up × 8 Up × 8 Up × 2 Up × 1.5 Up × 5 Stable Late response Evoline 1: has low salt tolerance Evoline 2: has high salt tolerance Evoline 3: has moderate salt tolerance Early response: 0.5 hours to 9 hours from induction Late response: 48 hours to 240 hours from induction

Example 3 Isolation of ABS Tolerance Genes of the Present Invention

RNA was extracted from 4 week-old tomato root and leaf tissues using Tri Reagent (Molecular Research Center, Inc), following the protocol provided by the manufacturer (www.mrcgene.com/tri.htm). Complementary DNA molecules were produced from the extracted mRNA using M-MuLV reverse-transcriptase (RT) enzyme (Roche) and T₁₆NN DNA primer, according to the manufacturer's instructions. The cDNA sequences set forth in SEQ ID NOs: 1, 4, 8-9 and 12-14, were amplified by PCR using the primers described in Table 11 below, with PFU proof reading DNA polymerase enzyme (Promega-www.promega.com/pnotes/68/7381_(—)07/7381_(—)07.html), following the protocol provided by the manufacturer. Additional restriction endonuclease sites were added to the 5′ prime end of each primer to facilitate cloning of the ABS tolerance genes of the present invention in binary vectors. TABLE 11 PCR primers used for amplifying ABS tolerance (ABST) genes of the present invention ABST Forward Reverse gene SEQ Primer Primer SEQ upstream downstream ID No SEQ ID No ID No restriction site restriction site 1 21 22 BamH1 SacI 4 23 24 BamH1 SacI 8 25 26 BamH1 SacI 9 27 28 XbaI SmaI 12 29 30 BamH1 SacI 13 31 32 BamH1 SacI 14 33 34 BamH1 SmaI

Example 4 Cloning the ABST Genes of the Present Invention

The resulting PCR blunt ended products were purified using PCR Purification Kit (Qiagen, Germany), digested with the appropriate restriction enzymes (Roche) and then inserted into the binary plasmid vector pPI. The plasmid pPI was constructed by inserting a synthetic poly-(A) signal sequence, originating from pGL3 basic plasmid vector (Promega, Acc No U47295; bp 4658-4811) into the HindIII restriction site of the binary vector pBI101.3 (Clontech, Acc. No. U12640).

The resulting pPI plasmid was digested with restriction enzymes (BamHI and SacI; MBI Fermentas) and purified using PCR Purification Kit (Qiagen, Germany). The open pPI construct was then ligated with each of the seven PCR products described hereinabove. The ligation was effected using a ligation mixture containing T4 DNA ligase enzyme (Roche) and was performed according to the manufacturer's instructions.

The pPI constructs harboring ABST genes of the present invention were introduced to E. coli DH5 competent cells by electroporation, using a MicroPulser electroporator (Biorad), 0.2 cm cuvettes (Biorad) and EC-2 electroporation program (Biorad). The treated cells were cultured in LB liquid medium at 37° C. for 1 hr, then plated over LB agar supplemented with kanamycin (50 mg/L; Sigma) and incubated at 37° C. for 16 hrs. Colonies which developed on the selective medium were analyzed by PCR using the primers set forth in SEQ ID NOs: 35-36, which were designed to span the inserted sequence in the pPI plasmid. The resulting PCR products were separated on 1.5% agarose gels and the DNA fragment having the predicted size were isolated and sequenced using the ABI 377 sequencer (Amersham Biosciences Inc) in order to verify that the correct DNA sequences were properly introduced to the E. coli cells.

Example 5 Generating Binary Vectors Comprising ABST Genes of the Present Invention and Plant Promoters Operably Linked Thereto

Generating binary vectors comprising the Cauliflower Mosaic Virus 35S promoter: The Cauliflower Mosaic Virus 35S promoter sequence (set forth in SEQ ID NO: 19) was inserted upstream of the ABST genes of the present invention in each of the pPI constructs described above. The promoter was isolated from the pBI121 plasmid (Clontech, Accession No. AF485783) using the restriction endonucleases HindIII and BamHI (Roche). The isolated promoter was ligated into the pPI constructs digested with the same enzymes. Altogether, seven pPI constructs were generated, each comprising the CaMV 35S promoter positioned upstream of the ABST genes of the present invention having a sequence set forth in SEQ ID NO: 1, 4, 8, 9, 12, 13 or 14.

Generating binary vectors comprising the At6669 promoter: The At6669 promoter sequence (set forth in SEQ ID NO: 20) was inserted upstream of the ABST genes of the present invention in each of the pPI binary constructs described above. The promoter was isolated from Arabidopsis thaliana var Col0 genomic DNA by PCR amplification using the primers set forth in SEQ ID NOs: 37-38. The PCR product was purified (Qiagen, Germany) and digested with the restriction endonucleases HindIII and BamHI (Roche). The resulting promoter sequence was introduced into the open binary constructs digested with the same enzymes. Altogether, seven pPI constructs were generated, each comprising the At6669 promoter positioned upstream of the ABST genes of the present invention having a sequence set forth in SEQ ID NO: 1, 4, 8, 9, 12, 13 or 14.

Example 6 Confirming At6669 Promoter Activity in Transgenic Arabidopsis Thaliana

The capacity of At-6669 promoter to regulate transcription of genes carried by the pPI vector in plants was tested. Accordingly, the promoter At6669 was inserted into the pPI binary vector upstream of a Luciferase reporter gene. The binary vector was introduced to Arabidopsis thaliana plants using the procedure as described in Example 6 below. Mature transformed T₂ Arabidopsis plants were assayed for bio-illumination in a darkroom using an ultra-low light detection camera (Princeton Instruments Inc., USA) using the procedure described by Meissner et al. (Plant J. 22:265, 2000). Illumination indicating positive Luciferase activity was observed in the flower and root meristem tissues of transformed plants (FIGS. 3A-D).

To study the regulation mode of the promoter under stress conditions, the 6669 promoter and 35S promoter were both fused to the Arabidopsis Rab7 gene. Rab7 expresssion under the 6669 promoter gave significantly higher salt and osmotic tolerance performance compared to 35S in Arabidopsis, as determined by vegetative growth.

The promoter was further validated by comparing tolerance level of Arabidopsis plants containing the ABST genes of the present invention under the regulation of 6669 and under the regulation of 35S promoter (FIG. 4). The plants were transformed with seven ABST genes of the present invention (ABST_(—)1, 6, 19, 22, 27, 36, 37) as described in Example 8. As illustrated in FIG. 4, the plant dry weight increased following transformation of the ABST genes under the 6669 promoter to a greater extent than following transformation of the ABST genes under the 35S promoter both under normal and stress (100 mM salt) conditions.

Example 7 Transforming Agrobacterium Tumefaciens Cells with Binary Vectors Harboring ABST Genes of the Present Invention

Each of the binary vectors described in Example 5 above were used to transform Agrobacterium cells. Two additional binary constructs, having the Luciferase reporter gene replacing an ABST gene (positioned downstream of the 35S or At6669 promoter), were used as negative controls.

The binary vectors were introduced to Agrobacterium tumefaciens GV301, or LB4404 competent cells (about 10⁹ cells/mL) by electroporation. The electroporation was effected by using a MicroPulser electroporator (Biorad), 0.2 cm cuvettes (Biorad) and EC-2 electroporation program (Biorad). The treated cells were cultured in LB liquid medium at 28° C. for 3 hr, then plated over LB agar supplemented with gentamycin (50 mg/L; for Agrobacterium strains GV301) or streptomycin (300 mg/L; for Agrobacterium strain LB4404) and kanamycin (50 mg/L) at 28° C. for 48 hrs. Abrobacterium colonies which developed on the selective media were analyzed by PCR using the primers set forth in SEQ ID NOs: 35-36, which were designed to span the inserted sequence in the pPI plasmid. The resulting PCR products were isolated and sequenced as described in Example 5 above, to verify that the correct ABST sequences were properly introduced to the Agrobacterium cells.

Example 8 Transformation of Arabidopsis Thaliana Plants with ABST Genes of the Present Invention

Arabidopsis thaliana Columbia plants (T₀ plants) were transformed using the Floral Dip procedure described by Clough and Bent (10) and by Desfeux et al. (11), with minor modifications. Briefly, T₀ Plants were sown in 250 ml pots filled with wet peat-based growth mix. The pots were covered with aluminum foil and a plastic dome, kept at 4° C. for 3-4 days, then uncovered and incubated in a growth chamber at 18-24° C. under 16/8 hr light/dark cycles. The T₀ plants were ready for transformation six days before anthesis.

Single colonies of Agrobacterium carrying the binary constructs, generated as described in Example 6 above, were cultured in LB medium supplemented with kanamycin (50 mg/L) and gentamycin (50 mg/L). The cultures were incubated at 28° C. for 48 hrs under vigorous shaking and then centrifuged at 4000 rpm for 5 minutes. The pellets comprising Agrobacterium cells were re-suspended in a transformation medium containing half-strength (2.15 g/L) Murashig-Skoog (Duchefa); 0.044 μM benzylamino purine (Sigma); 112 μg/L B5 Gambourg vitamins (Sigma); 5% sucrose; and 0.2 ml/L Silwet L-77 (OSI Specialists, CT) in double-distilled water, at a pH of 5.7.

Transformation of T₀ plants was effected by inverting each plant into an Agrobacterium suspension, such that the above ground plant tissue was submerged for 3-5 seconds. Each inoculated T₀ plant was immediately placed in a plastic tray, then covered with a clear plastic dome to maintain humidity and was kept in the dark at room temperature for 18 hrs, to facilitate infection and transformation. Transformed (transgenic) plants were then uncovered and transferred to a greenhouse for recovery and maturation. The transgenic T₀ plants were grown in the greenhouse for 3-5 weeks until siliques were brown and dry. Seeds were harvested from plants and kept at room temperature until sowing.

For generating T₁ and T₂ transgenic plants harboring the genes, seeds collected from transgenic T₀ plants were surface-sterilized by soaking in 70% ethanol for 1 minute, followed by soaking in 5% sodium hypochloride and 0.05% triton for 5 minutes. The surface-sterilized seeds were thoroughly washed in sterile distilled water then placed on culture plates containing half-strength Murashig-Skoog (Duchefa); 2% sucrose; 0.8% plant agar; 50 mM kanamycin; and 200 mM carbenicylin (Duchefa). The culture plates were incubated at 4° C. for 48 hours then transferred to a growth room at 25° C. for an additional week of incubation. Vital T₁ Arabidopsis plants were transferred to a fresh culture plates for another week of incubation. Following incubation, the T₁ plants were removed from culture plates and planted in growth mix contained in 250 ml pots. The transgenic plants were allowed to grow in a greenhouse to maturity. Seeds harvested from T₁ plants were cultured and grown to maturity as T₂ plants under the same conditions as used for culturing and growing the T₁ plants.

Example 9 Evaluating Growth of Transgenic Plants Cultivated Under Abiotic Stress Conditions

Methods:

T₁ or T₂ transgenic plants generated as described above were individually transplanted into pots containing a growth mixture of peat and vermiculite (volume ratio 3:2, respectively). The pots were covered for a 24 hr period for hardening, then placed in the greenhouse in random order and irrigated with tap water (provided from the pots' bottom every 3-5 days) for seven days. Thereafter, half of the plants were irrigated with a salt solution (100 mM NaCl and 5 mM CaCl₂) to induce salinity stress (stress conditions). The other half was irrigated with tap water throughout (normal conditions). All plants were grown in the greenhouse at 100% RH for 28 days and then harvested (the above ground tissue).

Vigor measurement: Fresh and dry mass were measured as a function of plant vigor. Dry mass was measured immediately following drying in an oven at 50° C. for seven days.

Results:

Fresh weight: No significant differences in plant fresh weights were observed between the T₁ plants transformed with 3 different ABST genes and plants transformed with the Luciferase reporter gene, grown either under normal or stress conditions (FIG. 5 and Table 12 below). Yet, T₁ plants transformed with SEQ ID NO: 1 positioned under the regulatory control of the At6669 promoter maintained 71% of their fresh weight when exposed to stress conditions, while the control plants (carrying Luciferase gene positioned under the regulatory control of the AT6669 promoter) maintained only 61% of their fresh weight under similar stress conditions. TABLE 12 Fresh weight of T₁ transgenic Arabidopsis plants irrigated with water or salt solution Transgene Irrigation (SEQ ID solution NO) Promoter N Rows¹ (mM NaCl) Mean (g) Std Error Luciferase At6669 2 0 0.7925 0.0275 Luciferase At6669 2 100 0.485 0.045 13  At6669 8 0 0.81625 0.020305 13  At6669 8 100 0.4725 0.029246 1 At6669 8 0 0.7875 0.026032 1 At6669 8 100 0.55875 0.044699 8 At6669 8 0 0.8575 0.023088 8 At6669 8 100 0.440625 0.011198 ¹N Rows represent number of independent transformation event plants measured. For each transgene, 3-5 independent transformation events with 1-3 plants per a single transformation event were used.

T₂ plants transformed with SEQ ID NOs: 7 or 14 positioned under the regulatory control of the 35S promoter accumulated significantly higher biomass than control plants, regardless of growth conditions. As shown in FIG. 6A and Table 13 below, the mean fresh weight of plants transformed with SEQ ID NOs: 7 and 14, grown under stress conditions, were 15% and 24%, respectively, higher than the mean fresh weight control plants grown under similar stress conditions. Similarly, the mean fresh weight of plants transformed with SEQ ID NOs: 7 or 14, grown under normal conditions, were 21% and 27%, respectively, higher than the mean fresh weight control plants grown under similar normal conditions.

Similar phenomenon was observed with T₂ plants transformed with SEQ ID NO: 4 positioned under the regulatory control of the 35S promoter. Accordingly, as shown in FIG. 6A and Table 13 below, the mean fresh weight of plants transformed with SEQ ID NO: 4 was 14% and 7% was higher than the mean fresh weight of control plants grown under stress and normal conditions, respectively. Similarly, T₂ plants transformed with SEQ ID NO: 4 positioned under the regulatory control of the At6669 promoter exhibited 1.3 and 5% higher biomass than control plants grown under stress and normal conditions, respectively (Table 14). However, these differences were not found statistically different under the experimental conditions. TABLE 13 Fresh weight of T₂ transgenic Arabidopsis plants irrigated with water or salt solution Transgene Irrigation (SEQ N solution ID NO) Promoter Rows (mM NaCl) Mean (g) Std Error Luciferase CaMV-35S 11 0 0.352727 0.011208 Luciferase CaMV-35S 11 100 0.280909 0.010484  9 CaMV-35S 11 0 0.426364 0.019599  9 CaMV-35S 11 100 0.322727 0.027306 12 CaMV-35S 11 0 0.374545 0.015746 12 CaMV-35S 11 100 0.249091 0.020647 1 CaMV-35S 8 0 0.36625 0.034171 1 CaMV-35S 8 100 0.265 0.031225 13 CaMV-35S 11 0 0.349091 0.013515 13 CaMV-35S 11 100 0.293636 0.019921 14 CaMV-35S 11 0 0.446364 0.025558 14 CaMV-35S 11 100 0.348182 0.023772  8 CaMV-35S 11 0 0.310909 0.015223  8 CaMV-35S 11 100 0.253636 0.01539  4 CaMV-35S 11 0 0.379091 0.010992  4 CaMV-35S 11 100 0.318182 0.013336 Table 13 continued ¹N Rows represent number of independent transformation event plants measured. For each transgene, 3-5 independent transformation events with 1-3 plants per a single transformation event were used.

T₂ plants transformed with SEQ ID NOs: 1 and 13 positioned under the regulatory control of the At6669 promoter and grown under stress conditions, exhibited significantly higher biomass than control plants grown under similar stress conditions. The mean fresh weight of T₂ plants transformed with SEQ ID NOs: 1 and 13 positioned under the regulatory control of the At6669 promoter, and grown under stress conditions, were 37% and 21%, respectively, higher than the mean fresh weight control plants grown under similar stress conditions (FIG. 6B and Table 14 below). No significant increase in biomass over control was observed when these transgenic plants (carrying SEQ ID NOs: 1 and 13 regulated under At6669 promoter) where grown under normal conditions. TABLE 14 Fresh weight of T₂ transgenic Arabidopsis plants irrigated with water or salt solution Transgene Irrigation (SEQ solution (mM ID NO) Promoter N Rows NaCl) Mean (g) Std Error Luciferase At6669 6 0 0.3 0.010328 Luciferase At6669 6 100 0.125 0.009916 13  At6669 6 0 0.286667 0.024449 13  At6669 6 100 0.151667 0.007032 1 At6669 6 0 0.305 0.03423 1 At6669 6 100 0.171667 0.012225 4 At6669 6 0 0.315 0.049983 4 At6669 6 100 0.126667 0.005578 12  At6669 6 0 0.263333 0.012824 12  At6669 6 100 0.098333 0.007923 8 At6669 6 0 0.228333 0.020235 8 At6669 6 100 0.121667 0.004014 ¹N Rows represent number of independent transformation event plants measured. For each transgene, 3-5 independent transformation events with 1-3 plants per a single transformation event were used.

The results illustrate that the isolated ABST genes of the present invention, set forth in SEQ ID NOs: 1 and 13, are capable of increasing plant tolerance to abiotic stress, such as a salinity stress. In addition, the isolated ABST genes of the present invention as set forth in SEQ ID NOs: 7, 14 (and possibly also 4), are capable of substantially promoting biomass in plants grown under stress, as well as under normal conditions.

Dry mass: Table 15 summarises the results the dry mass of T1 plants grown under 100 mM NaCl. TABLE 15 Dry mass of T1 plants grown under 100 mM Nacl Relative dry mass compared to control Gene name Mean (g) Std Error (%) Pver + 6669 (negative 0.05635 0.00674 100 control) Rab7 positive control) 0.0656 0.00674 117.1428571 ABST_1 0.074417 0.00389 132.8875 ABST_19 0.054567 0.00389 97.44107143 ABST_36 0.059117 0.00389 105.5660714

Table 16 summarises the results of the absolute and relative dry mass of the of the T2 transgenic lines overexpressing the ABST genes under regular growth conditions. TABLE 16 Summary of absolute (g) and relative dry mass (relative to negative control %) of the T2 transgenic lines overexpressing the ABST genes under regular growth conditions T2 plants overexpressing T2 plants overexpressing the ABST gene the ABST gene under the 35S promoter under the 6669 promoter Mean dry Relative Mean dry Relative Gene name mass (g) Std Error expression % mass (g) Std Error expression % Negative control 0.048666667 0.006557 100 0.0391 0.006154 100 ABST_1 0.056416667 0.007331 117.534722 0.05790333 0.006251 148.4700854 ABST_6 0.052666667 0.006557 109.722222 0.0561 0.006154 143.8461538 ABST_19 0.0432 0.006557 90 0.03553333 0.006251 91.11111103 ABST_22 0.066 0.006557 137.5 ND ND ND ABST_36 0.049333333 0.006557 102.777778 0.0484 0.006154 124.1025641 ABST_37 0.0632 0.006557 131.666667 ND ND ND

As summarized in Table 16 above, transgenic T₂ Arabidopsis plants over-expressing ABST genes of the present invention as set forth in SEQ ID NOs: 1 (ABST_(—)1) and 4 (ABST_(—)6) showed significant elevation of dry mass both under the 35S promoter and the 6669 promoter (ABST_(—)1: 18%, 49% respectively, ABST_(—)6: 10%, 44% respectively). SEQ ID NO: 13 (ABST_(—)36) over-expression caused elevation in dry mass only under the regulation of 6669 promoter (24%). ABST_(—)22 and _(—)37 over-expression (SEQ ID NOs: 9 and 14 respectively), under the regulation of the 35S promoter, caused more than a 40% increase in the dry mass of the transgenic lines.

The results showed that all five tested genes improve vegetative growth development under favorable conditions. ABST_(—)1 and 6 improve plant vigor in both regulation modes (6669 and 35S promoters).

The specific gene-promoter combination has a significant effect on dry mass elevation.

To further examine if elevation in plant vigor has a direct effect on total seed weight, T₂ plant seeds (grown under regular conditions) over-expressing ABST 1, (SEQ ID NO: 1) 6 (SEQ ID NO: 4), 36 (SEQ ID NO: 13) and 37 (SEQ ID NO: 14) under the 6669 promoter were weighed. The seeds from plants over-expressing ABST_(—)1 and 36 weighed 50% more compared to control lines as illustrated in FIG. 7 and Table 17 below. TABLE 17 Average seed weight of arabidopsis lines over-expressing ABST genes 1, 6, 19, 36, 37 under the 6669 promoter Least Sq Level of Level of Std Level Mean significance* significance* Error ABST_1 0.062 A 0.006 ABST_36 0.061 A 0.005 ABST_37 0.053 A B 0.004 ABST_6 0.048 A B 0.006 Negative control 0.048 A B 0.005 Positive control-Rab7 0.043 B 0.005 ABST_19 0.043 B 0.004 *Levels not connected by same letter are significantly different

The effect of over-expression of ABST genes in plants subjected to salt stress on dry mass was tested using the same plant populations grown under continuous irrigation of saline water.

As summarized in Table 18 below, ABST_(—)6 and 36 (SEQ ID NOs: 4 and 13 repectively) increased the plant dry mass under both the 35S and 6669 promoters (ABST_(—)6: 25%, 16% respectively; ABST_(—)36: 15%, 33% respectively). Plants over-expressing ABST_L (SEQ ID NO: 1) showed higher dry mass only under the 6669 promoter (66%). ABST_(—)22 and 37 (SEQ ID NOs: 9 and 14 repectively) were tested only under the 35S promoter and showed a significant increase (>43%) of plant dry mass compared to control line. TABLE 18 Summary of absolute (g) and relative dry mass (relativ to negative control %) of the T2 transgenic lines overexpressing the ABST genes under salt stress conditions T2 plants overexpressing T2 plants overexpressing the ABST gene under the the ABST gene under the 35S promoter 6669 promoter Mean Relative Mean Relative dry expression dry expression mass Std compare to mass Std compare to Gene name (g) Error control (%) (g) Error control (%) Negative 0.041 0.005 100.000 0.019 0.002 100.000 control ABST_1 0.035 0.006 93.280 0.032 0.002 166.035 ABST_6 0.052 0.005 124.750 0.022 0.001 114.480 ABST_19 0.040 0.005 102.273 0.017 0.002  87.753 ABST_22 0.056 0.005 142.455 ND ND ND ABST_36 0.049 0.005 115.910 0.027 0.002 132.576 ABST_37 0.059 0.005 143.068 ND ND ND ND = not determined

Table 19 below summarizes the results of all the dry mass and seed measurements that were performed on the transgenic arabidopsis over-expressing the ABST genes. (calculated as percentage compare negative control). TABLE 19 Dry Mass and seed measurements Growth conditions Measurement/Gene name ABST_1 ABST_6 ABST_22 ABST_36 ABST_37 Favorable Increase (%) of dry mass of plant over 18 10 38 0 32 conditions expressing ABST genes under 35S promoter Favorable Increase (%) of dry mass of plant over 49 44 ND 24 ND conditions expressing ABST genes under 6669 promoter Favorable Increase of seeds weight in plants over 28 0 ND 27 11 conditions expressing ABST genes under 6669 regulation Salt stress Increase of dry mass of plant over 66 14 ND 33 ND conditions expressing ABST genes under 6669 regulation Salt stress Increase of dry mass of plant over 0 25 42 16 43 conditions expressing ABST genes under ABST 35S regulation Table 19 continued

Example 10 Evaluating Growth of Transgenic Tomato Plants Cultivated Under Abiotic Stress Conditions

The M82 tomato variety strain (Evoline 3) was used to determine whether improvement of plant vigor under stress may be translated into improvement of commercial yield. ABST genes 1, 6 and 36 (SEQ I.D. NOs. 1, 4 and 13 respectively) were transformed under the regulation of the 6669 promoter. As described in Example 9, all three gene combinations showed significant improvement of stress tolerance in arabidopsis plants. The genes were introduced into M82 variety by crossing transgenic miniature tomato lines with M82 plants. To represent the variation of the position effect, a pool of pollen from transgenic lines representing 4 different insertion events from each one of the genes were used as the male parent. The F1 hybrids were used for further evaluation.

The segregating F1 populations were divided into two isogenic populations, i.e. plants over-expressing the ABST genes of the present invention and plants that were not transformed to over-express ABST genes (NT) from the same populations used as negative controls. During the first three weeks, all the plants were grown in a nursery under regular conditions. Following this period the plants were transplanted into a commercial greenhouse under two different treatments. The first group of plants was grown under favorable conditions while the second group was grown under continuous irrigation of saline water (180 mM NaCl). Each transgenic line was compared to a NT plant derived from the same F1 population. The plants were evaluated for their plant and fruit performance at a stage where the percentage of red fruit was on average 80%.

Results:

The plants over-expressing ABST genes showed improved vigor and larger root systems than the NT plants. In addition, the plants over-expressing ABST genes showed improved yield under salt stress conditions.

Specifically, plants over-expressing ABST genes showed an elevation in the fresh weight of both canopies and roots. The populations expressing ABST_(—)1, 6 and 36 showed elevations of 165%, 162%, 206% respectively in canopy fresh weight compared to NT populations (Table 20) and higher root weight of 162%, 168% and 121% respectively compared to NT plants. TABLE 20 Summary of absolute (g) and relative fresh mass (relative to negative control %) of the canopies of M82 tomato T2 transgenic lines overexpressing the ABST genes under saline water irrigation M82 tomato T2 plants overexpressing the ABST gene under the 6669 promoter Mean Relative canopies increase fresh Std Level of compare to Gene name weight Error significancy* control(%) [MT]x[M82]_T 142.780 26.375 c 99.986 (transgenic negative control) Plasmid backbone only) [ABST_1]x[M82] 235.780 32.302 ab 165.112 [ABST_6]x[M82] 231.280 45.682 abc 161.961 [ABST_36]x[M82] 294.168 52.263 a 206.000 *Levels not connected by same letter are significantly different)

To further prove that this elevation in weight was due to accumulation of biomass and not only due to water accumulation, the dry mass of both the canopies and roots was measured. The dry mass of the canopies increased by 156%, 145% and 161% in the lines expressing ABST_(—)1, 6, 36 respectively compared to the corresponding NT lines. Similar effects were observed in the roots of these lines. Roots of the plants over-expressing ABST genes contained 40% (as summarized in Table 21 below) more dry matter than roots of the NT control plants (ABST_(—)1-168%, 6-159% and 36-140%). TABLE 21 Summary of absolute (g) and relative dry mass (relative to negative control %) of the roots of M82 tomato T2 transgenic lines overexpressing the ABST genes under saline water irrigation M82 tomato T2 plants overexpressing the ABST under the 6669 promoter Relative increase Mean compare root dry Level of to control Gene name weight (g) Std Error significancy* (%) [MT]x[M82]_T 2.073 0.310 b 100.000 (transgenic negative control) [ABST_1]x[M82] 3.700 0.379 a 168.182 [ABST_6]x[M82] 3.500 0.424 a 159.091 [ABST_36]x[M82] 3.067 0.693 ab 139.394 *Levels not connected by same letter are significantly different)

Only transgenic plants over expressing ABST_(—)36 had a lower root/shoot mass ratio than control plants (Table 22 below). This lower ratio (0.067 compared to more than 0.08 in control plants) is the result of a nearly 50% increase in shoot fresh weight rather than a major decrease in root fresh weight. This finding suggests that under stress growth conditions, the ABST_(—)36 over-expressing plants require a relatively lower root mass to support shoot growth and development. TABLE 22 Ratio between root to shoot mass in control plants and three transgenic lines over expressing ABST_1, 6, 36 Gene name Ratio dry weight roots per canopy [MT]x[M82] 0.086287522 Non-transgenic negative control [ABST_1]x[M82] 0.083090052 [ABST_6]x[M82] 0.085003036 [ABST_36]x[M82] 0.067

Fruit yield was analyzed by measuring the number of fruit clusters, the number of green and red fruits and weight of the green and red fruits in each one of the lines.

Plants over-expressing ABST_(—)36 comprise (37%) significantly more fruit clusters compared to control line suggesting a link between vigor and yield potential as summarized in Table 23 below.

All three tested ABST genes of the present invention improved total fruit yield as illustrated in Table 24. Specifically, ABST_(—)1 increased fruit yield by 137%. ABST_(—)6 increased fruit yield by 151%. ABST_(—)36 increased fruit yield by 191%. The relative large internal variation within populations reflects the variation that exists between different insertion events.

A more detailed analysis of the yield determinants showed that most of the additional yield (50% to 90%) was due to elevation in the weight of green fruit (Table 25). In addition most of the elevation in yield was due to an increase in the number of fruits rather than enlargement of fruit size (Table 26).

The significant difference in the number of green fruits between the lines largely depends on the physiological status of the plants. The control NT plants wilted much earlier while the plants over-expression ABST genes continued to develop for a longer period. TABLE 23 Average number of fruit clusters in transgenic lines over-expressing the ABST genes and control lines M82 tomato T2 plants overexpressing the ABST gene under the 6669 promoter Mean number of Level of Relative per Gene name clusters Std Error significant control (%) [MT]x[M82]_T 18.586 1.493 b 100.000 (Transgenic negative control) [ABST_1]x[M82] 19.402 1.829 ab 104.874 [ABST_6]x[M82] 22.533 2.586 ab 121.799 [ABST_36]x[M82] 25.467 2.876 a 137.660

TABLE 24 Total fruit yield in transgenic lines over-expressing the ABST genes and control lines M82 tomato T2 plants overexpressing the ABST gene under the 6669 promoter Mean of total fruits Level of Relative per Gene name weight (g) Std Error significant control (%) [MT]x[M82]_T 431.974 61.573 c 100.000 (Transgenic negative control) [ABST_1]x[M82] 592.724 71.693 bc 137.104 [ABST_6]x[M82] 652.338 101.389 bc 148.869 [ABST_36]x[M82] 825.934 115.330 b 187.029

TABLE 25 Green fruit weight of transgenic lines over-expressing the ABST genes and control lines (gram) M82 tomato T2 plants overexpressing the ABST gene under the 6669 promoter Mean of green fruits Level of Relative per Gene name weight (g) Std Error significant control (%) [MT]x[M82]_T 145.401 47.168 c 100.000 (Transgenic negative control) [ABST_1]x[M82] 221.722 55.219 bc 152.491 [ABST_6]x[M82] 256.431 78.091 bc 176.362 [ABST_36]x[M82] 421.925 87.206 b 290.182

TABLE 26 Average number of the green fruits that were produced in the transgenic lines over- expressing the ABST genes and control lines M82 tomato T2 plants overexpressing the ABST gene under the 6669 promoter Mean of number of Std Level of Relative per Gene name green fruits Error significant control (%) [MT]x[M82]_T 26.127 6.173 bc 100.000 (Transgenic negative control) [ABST_1]x[M82] 41.666 7.146 ab 160.254 [ABST_6]x[M82] 41.047 10.106 ab 157.875 [ABST_36]x[M82] 58.703 11.756 a 225.780

FIGS. 8A-D depict control and transgenic plants of the present invention illustrating the increase in yield following over-expression of the ABST genes of the present invention.

Comparison between lines expressing ABST_(—)1, 6, 36 under favorable conditions to control lines under favorable conditions did not show any significant changes in the vigor of the vegetative parts or in the fruit yield. The following parameters were tested: fresh and dry weight of the roots and canopies, green fruit weight, red fruit weight and the average green and red fruit diameter. In all these parameters no differences were detected.

Table 27 below summarizes the results on crop yield following over-expression of ABST in tomato plants. TABLE 27 Comparison of plant and fruit performances between transgenic and control plants grown under favorable and salt stress conditions (irrigation of 180 Mm NaCl) Control ABST_1 ABST_6 ABST_36 Control ABST_1 ABST_6 ABST_36 (180 mM (180 mM (180 mM (180 mM (Water) (Water) (Water) (Water) NaCl) NaCl) NaCl) NaCl) Canopy ND ND ND ND 143 c 236 ab 231 ab 295 a fresh weight Root  84 a  74 a  72 a  87 a  16 c  27 a  28 a  20 ab fresh weight Number  195 a  185 a  186 a  171 a  66 c  90 bc  87 bc 104 b of fruits per plant Total 2750 a 2845 a 2846 a 2501 a 432 c 593 bc 652 bc 826 b Fruit weight per plant

Tomato plants that were crossed between transgenic miniature tomatos and the M82 line (line 3) were also grown under both salt stress and favorable conditions. The salt stress was carried out by continuous irrigation of saline water containing 180 mM NaCl.

The miniature populations expressing ABST_(—)1 and 22 showed the highest improvement in salt tolerance compare to the control line based on plant and root mass and yield performance. The dry mass of the transgenic lines expressing ABST_(—)1, 22 was increased by 300% and 257% respectively. ABST_(—)36 improved both shoot mass and yield by about 30% as compared to control plants. The lines expressing ABST_(—)1 and 22 showed the highest yield performance (165% and 140% respectively) compared to control population.

ABST 36 and 37 were also over-expressed in a line 2 tolerant tomato plant (Y361) and its expression was compared to that in a line 1 sensitive tomato plant (Shirly). As illustrated in FIGS. 9A-C, ABST_(—)36 expression was higher in the tolerant plants in both roots and leaves. ABST_(—)37 was up-regulated in leaves of both tolerant and sensitive lines. However in the tolerant line (line 2) the expression was up-regulated in leaves much faster than in leaves of sensitive line (line 1). Up-regulation in roots occurred only in the tolerant lines (line 2).

Hence, the results from Examples 1-10, clearly indicate that the abiotic stress tolerance genes of the present invention described herein can be readily isolated and utilized to substantially increase tolerance to abiotic stress and/or biomass in plants.

Example 11 Identifying Putative Abiotic Stress-Tolerance Genes from Monocots

Monocot ortholog sequences for the 5 putative ABST tomato genes (SEQ I.D. NOs. 1, 4, 9, 13 and 14) were sought. Monocot genomic databases namely NCBI (http://www.ncbi.nlm.nih.gov/) and TIGR (http://www.tigr.org/) databases of Maize, Sorghum and Barley were initially screened. The expressed sequence tags (ESTs) and cDNA sequences were clustered and assembled using the LEADS™ software (Compugen) and compared to the TIGR (http://www.tigr.org/) databases of the above monocots. Overall, clustering of 372,000 maize ESTs resulted in 41,990 clusters among them 19,870 singletons. In Sorghum, about 190,000 ESTs were clustered into 39,000 clusters while in barley 370,500 ESTs generated 50,000 different clusters each representing a different gene. A digital expression profile summary was compiled for each cluster according to all keywords included in the sequence records comprising the cluster.

Yet, while comparing the monocot sequences to the tomato ABST genes, sequence homology levels differed dramatically, ranging from 45% to 88%. Moreover, the in-silico expression profile of the monocot genes did not always fit the profile of a gene involved in ABS tolerance.

In an attempt to identify the best orthologues for the tomato ABST genes various additional factors were analyzed. First, the sequences of the 5 tomato ABST genes (SEQ ID NO: 1, 4, 9, 13 and 14) and their deduced polypeptide sequences (SEQ ID NOs: 236-240) were compared to all monocot putative proteins, encoded by DNA sequences of gene clusters mentioned above. The comparison was performed on the protein level looking for identity higher than 45% along the entire protein sequences. Table 28 shows the best homologous genes and their identity level to the tomato ABST proteins. Next, these monocot proteins originating from different monocot species (barley, sorghum and maize) were screened based on their expression pattern during the development of several monocot species. This screening was based on digital expression of the genes, as described above. The genes were selected based on three criteria: genes with higher expression in roots, roots and leaves and or induce expression by treatments representing soil stress conditions (drought, salinity, soil deficiencies). The increase of expression was only counted in cases where the increase was greater than 2 fold (relative to the random EST distribution) with significance probability lower than 0.05. Table 29 summarizes the expression profile of the genes in different organ or tissues and the treatments that set off significant elevation in their expression level. TABLE 28 The level of homology between the tomato ABST genes and their homologs from monocots % Identity (Percenrtage Tomato from gene TIGR Name/Acc Level of the entire SEQ No of homology protein ID NO Homologous gene Plant origin (e value) sequence) 1 TC104838 Sorghum 2E−70 88% SEQ ID NO: 93 TC103857 Sorghum 2E−70 88% TC258871 Maize 1E−69 86% TC139195 Barley 5E−69 86% 4 TC94284 Sorghum 3E−43 45% SEQ ID NO: 94 TC132394 Barley 6E−40 44% 9 TC93449 Sorghum 1E−99 58% SEQ ID NO: 95 TC146720 Barley 3E−99 58% 13 TC92953 Sorghum 7E−59 47% SEQ ID NO: 96 TC91426 Sorghum 4E−98 74% SEQ ID NO: 97 TC91474 Sorghum 5E−98 72% TC263205 Maize 2E−97 74% 14 TC103772 Sorghum 1E−52 49% SEQ ID NO: 98 TC148356 Barley 1E−54 46% TC260731 Maize 1E−54 46%

TABLE 29 The expression profile of ABST homologous in silico genes as represented by statistical analysis of their EST distribution Fold increase (All results Fold increase Name of Organs/tissues are Treatments that (all results are Homologous with the highest singnificant induce th

singnificant in gene Plant species gene expression in P value >0.05) expression level P value >0.05) TC104838 Sorghum Pollen preanthesis 3 Ethylene, 2 SEQ ID NO: 93 stage drought TC103857 Sorghum Diverse 2 None*  None* expression TC258871 Maize Diverse 2 None*  None* expression, preferentially in cell lignification region of leaves TC139195 Barley In various grain 2-3.5 None None tissues TC94284 Sorghum Leaves, 4.5 Drought, 4 SEQ ID NO: 94 roots during fruit 2 nitrogen 2 loading deficiencies, 2 soil acidity TC132394 Barley Leaves, coleoptile 2.5 None None mainly during 3 fruit development TC93449 Sorghum Flowers ovary 3 Salinity stress 4 SEQ ID NO: 95 TC146720 Barley Seeds 2 Cold stress, 3 preferentially in Fusarium 3.5 the embryo and infection scutellum during ripening TC92953 Sorghum Leaves during 2 Drought, 4 SEQ ID NO: 96 fruit loading Nitrogen- 4 deficiency, 2.5 salinity (150 Mm) TC91426 Sorghum Young roots 12 Ethylene, 4 SEQ ID NO: 97 etiolation, soil 3 acidity 12 TC91474 Sorghum Entire seedling 2 Etiolation 16 TC263205 Maize Primary root 3 Drought 2 system in seedling stage TC103772 Sorghum Young roots 2 Drought, 2 SEQ ID NO: 98 soil acidity 2 TC148356 Barley Callus, leaves in 4, 2 Infection by 2 the vetatative Blumeria stage graminis TC260731 Maize Root preferntialy 2.5 None None primary roots Table 29 continued None* - None of the treatments with significant elevation in digital expression could be considered as soil stress treatment

A combination of the above screening as described in Table 28 and in Table 29 revealed the final list of six monocot genes that are predicted to be the most related to the tomato ABST genes (SEQ ID NOs. 93, 94, 95, 96, 97 and 98).

Another type of sequence alignment for finding putative orthologous sequences from barley, rice, maize and sorghum, using the tomato ABST genes as involved the use of an evology system. Digital expression analysis was performed on these genes allowing for the identification of other putative monocot orthologs. The results were corroborated by phylogenetic analysis which studies the relationships between the tomato ABST genes and the putative monocot orthologs.

The Evology system is a method for constructing ortholog groups across multiple eukaryotic taxa, using the Markov cluster algorithm to group putative orthologs and paralogs. The method coherent with the groups identified by EGO (http://www.tigr.org/tdb/tgi/ego/index.shtml) but improved the identification of “recent paralogs” since EGO is easily misled by the functional redundancy of multiple paralogs and by the absence of true orthologs within incomplete genome data set as in most of the plant species.

The Evologs is a tool for large-scale automated eukaryotic ortholog group identification. To resolve the many-to-many orthologous relationships inherent in comparisons across multiple genomes, Evologs applied the Markov Cluster algorithm (http://micans.org/mcl/), which is based on probability and graph flow theory and allows simultaneous classification of global relationships in a similarity space. MCL simulates random walks on a graph using Markov matrices to determine the transition probabilities among nodes of the graph. The MCL algorithm has previously been exploited for clustering a large set of protein sequences, where it was found to be very fast and reliable in dealing with complicated domain structures. Evologs generates clusters of at least two proteins, where each cluster consists of orthologs or paralogs from at least one species.

The putative orthologs were obtained using three levels of stringency. The first group with the lowest level (p value <=1e-20 and identity >=50%), the second group with moderate level of stringency (p value <=1e-42 and identity >=50%) and the third group with the highest stringency include p value <=1e-70 and identity >=70%.

-   1. Eight genes were identified as putative orthologs for ABST_(—)1.     This group was defined using the highest stringency parameters     (highest cutoff—level 3). -   2. Nine monocot genes were identified as ABST_(—)6 putative     orthologs. These genes were found only after filtering under the     lowest stringency alignment (level 1) parameters. This reduces the     probability of finding a real monocot ortholog. -   3. Eight monocot genes were identified as ABST_(—)22 putative     orthologs. These genes were found by using the highest stringency     parameters (highest cutoff—level 3). -   4. Twenty three putative ortholog genes were found for ABST_(—)36     (Table 2). This group was found by using the highest stringency     parameters (the highest cutoff—level 3). -   5. Fourteen putative orthologs for ABST_(—)37 were found only after     reducing the alignment parameters to the second stringency level.     However since the genes are transcription factors more accurate     comparison should be done on their binding domains.

These genes were subjected to digital expression analysis. Genes that were identified as being up-regulated under stress conditions underwent phylogenetic analysis. The phylogenetic trees showed similar distances between tomato, Arabidopsis and monocots supporting the claim that conservation in function in Arabidopsis and tomato strongly indicates conservation in function in monocot (data not shown).

A final list of ten candidate monocot ortholog genes was drawn up, as detailed in Table 30 below. TABLE 30 List of ten candidate monocot orthologues as revealed by evolog analysis, phylogenetic analysis and digital expression analysis % Identity TIGR (Percentage from the Tomato gene Name/Acc No of entire protein SEQ ID NO: Homologous gene Plant origin sequence) 1 TC104838 Sorghum 88% SEQ ID NO: 93 4 TC94284 Sorghum 45% SEQ ID NO: 94 9 TC93449 Sorghum 58% SEQ ID NO: 95 TC102291 Sorghum 54% SEQ ID NO: 241 13 TC131030 Barley 72% SEQ ID NO: 242* AF057183 maize 70% SEQ ID NO: 245 TC249365 maize 70% SEQ ID NO: 244 TC249366 maize 70% SEQ ID NO: 243 TC263205 Maize 74% SEQ ID NO: 246 14 TC103772 Sorghum 49% SEQ ID NO: 98 *SEQ ID NO: 242 is identical to SEQ ID NO: 74

The digital expression profile for TC104838 (SEQ ID NO:93) is listed in Tables 31-33 herein below. TABLE 31 Expression of TC104838 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flower 3 26937 1.11986 2.6789 0.0865946 pollen 3 8840 1 3 0.00431486 leaf 1 17487 1 1 0.535872 seedling 2 95402 3.96618 0.504263 0.970844

TABLE 32 Expression of TC104838 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 4 32705 1.35966 2.94192 0.0301425 8-14 days pre- 3 8840 1 3 0.00431486 anthesis post-flowering 1 5768 1 1 0.216515 germination 2 104379 4.33939 0.460895 0.985772 1.5 week 2 47911 1.99182 1.00411 0.636908 vegetative 1 21465 1 1 0.615042 5 weeks old 1 9746 1 1 0.34123

TABLE 33 Expression of TC104838 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 2 18855 1 2 0.180136 drought stress 1 5768 1 1 0.216515 after flowering drought stress, 1 9746 1 1 0.34123 7, 8 days after water witheld hormone 2 26047 1.08286 1.84696 0.29656 treatment ethylene- 2 6261 1 2 0.0256292 induced with ACC, 27 and 72 hours after induction

The digital expression profile for TC94284 (SEQ ID NO:94) is listed in Tables 34-36 herein below. TABLE 34 Expression of TC94284 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value leaf 5 17487 1.14242 4.37668 0.0032544 seedling 6 95402 6.23257 0.962684 0.675068 leaf 2 19738 1.28947 1.55102 0.375678 root 2 7258 1 2 0.078916

TABLE 35 Expression of TC94284 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 4 32705 2.1366 1.87213 0.148602 post-flowering 4 5768 1 4 0.000374052 germination 6 104379 6.81904 0.87989 0.795559 1.5 week 2 47911 3.13001 0.638976 0.864874   2 weeks old 4 27953 1.82616 2.19039 0.094453 vegetative 1 21465 1.4023 0.713114 0.7769   4 weeks old 1 8221 1 1 0.423423

TABLE 36 Expression of TC94284 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 4 18855 1.23179 3.24731 0.0271328 drought stress 4 5768 1 4 0.000374052 after flowering nutrient 2 9927 1 2 0.134282 deficiencies Nitrogen 2 3313 1 2 0.0189181 deficient pathogen 3 17272 1.12837 2.6587 0.0951298

The digital expression profile for TC93449 (SEQ ID NO:95) is listed in Tables 37-39 herein below. TABLE 37 Expression of TC93449 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value callus 2 9585 1.36622 1.46389 0.40017 cell 2 9585 1.36622 1.46389 0.40017 suspension flower 6 26937 3.83953 1.56269 0.17419 ovary 4 9434 1.3447 2.97465 0.0426186 leaf 3 17487 2.49255 1.20359 0.461176 seedling 13 95402 13.5983 0.955999 0.676721 leaf 1 19738 2.8134 0.355442 0.949846 root + leaf 5 19261 2.74541 1.82122 0.131853 callus 2 9585 1.36622 1.46389 0.40017 Table 37 continued

TABLE 38 Expression of TC93449 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 7 32705 4.66168 1.5016 0.169309   8 weeks old 4 9434 1.3447 2.97465 0.0426186 (immature) post-flowering 1 5768 1 1 0.56683 pre-anthesis 2 8663 1.2348 1.6197 0.352104 germination 13 104379 14.8779 0.873779 0.841438   1 week 1 19538 2.78489 0.35908 0.948201 1.5 week 11 47911 6.8291 1.61075 0.0526309   2 weeks old 1 27953 3.98435 0.250982 0.987187 vegetative 2 21465 3.05956 0.653688 0.82924   4 weeks old 2 8221 1.1718 1.70678 0.328675

TABLE 39 Expression of TC93449 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 1 18855 2.68754 0.372087 0.942184 drought stress 1 5768 1 1 0.56683 after flowering heat stress 1 8875 1.26502 0.790502 0.727378 4 and 24 hours 1 8875 1.26502 0.790502 0.727378 at 40-42° C. hormone 6 26047 3.71267 1.61609 0.155303 treatment ethylene- 4 6261 1 4 0.0111844 induced with ACC, 27 and 72 hours after induction Salicylic acid- 2 4793 1 2 0.148347 treated nutrient 1 9927 1.41497 0.70673 0.767414 deficiencies Iron deficient 1 3353 1 1 0.382937 pathogen 3 17272 2.4619 1.21857 0.452792 Resistant 1 9051 1.29011 0.775131 0.734507 plants, 48 h after Colletotrichum graminicola innoculation (fungi) Susceptible 2 8221 1.1718 1.70678 0.328675 plants, 48 h after Colletotrichum graminicola innoculation (fungi) salinity 4 6080 1 4 0.010119 150 mM NaCl 4 6080 1 4 0.010119 for 3, 6, 12 and 24 hr Table 39 continued

The digital expression profile for TC102291 (SEQ ID NO: 241 and 247) is listed in Tables 40-42 herein below. TABLE 40 Expression of TC102291 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value callus 4 9585 1.48007 2.70257 0.0576229 cell 4 9585 1.48007 2.70257 0.0576229 suspension leaf 5 17487 2.70026 1.85167 0.126138 seedling 14 95402 14.7315 0.950342 0.688991 leaf 2 19738 3.04785 0.6562 0.825957 root + leaf 9 19261 2.97419 3.02603 0.00168405

TABLE 41 Expression of TC102291 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 3 32705 5.05016 0.594041 0.904756 post-flowering 3 5768 1 3 0.0581305 germination 14 104379 16.1177 0.868609 0.854646   1 week 2 19538 3.01697 0.662917 0.821366 1.5 week 4 47911 7.3982 0.540672 0.962528   2 weeks old 8 27953 4.31637 1.85341 0.0543811 vegetative 5 21465 3.31453 1.50851 0.230885   5 weeks old 3 9746 1.50493 1.99344 0.188518 pre-flowering 2 3341 1 2 0.0935317

TABLE 42 Expression of TC102291 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 8 18855 2.9115 2.74772 0.00599968 drought stress 3 5768 1 3 0.0581305 after flowering drought stress 2 3341 1 2 0.0935317 before flowering drought stress, 3 9746 1.50493 1.99344 0.188518 7, 8 days after water witheld heat stress 1 8875 1.37044 0.729694 0.755364 4 and 24 hours 1 8875 1.37044 0.729694 0.755364 at 40-42° C. hormone 6 26047 4.02206 1.49177 0.204473 treatment Abscisic acid- 5 4306 1 5 0.000458231 treated ethylene- 1 6261 1 1 0.626674 induced with ACC, 27 and 72 hours after induction light response 1 18685 2.88525 0.34659 0.953042 etiolated 1 10663 1.64653 0.607337 0.817519 nutrient 1 9927 1.53288 0.652366 0.794035 deficiencies Nitrogen 1 3313 1 1 0.403524 deficient pathogen 2 17272 2.66706 0.749889 0.761847 Resistant 2 9051 1.39761 1.43101 0.411127 plants, 48 h after Colletotrichum graminicola innoculation (fungi) salinity 3 6080 1 3 0.0659796 150 mM NaCl 3 6080 1 3 0.0659796 for 3, 6, 12 and 24 hr Table 42 continued

The digital expression profile for TC131030 (SEQ ID NO:242 and 248) is listed in Tables 43-45 herein below. TABLE 43 Expression of TC131030 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value root 5 16560 1 5 1.48052E−06 seedling 1 57039 1 1 0.662622 root 1 1988 1 1 0.0341428 shoot 1 8317 1 1 0.136442

TABLE 44 Expression of TC131030 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value germination 1 92778 1.61655 0.6186 0.847952 5-8 days 1 29670 1 1 0.417607 seedling 5 33561 1 5 4.84613E−05 3 weeks old 5 21898 1 5 5.90628E−06

TABLE 45 Expression of TC131030 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 3 8410 1 3 0.00027555 drought 2 4939 1 2 0.00296904 stressed drought 1 1496 1 1 0.0257848 stressed (6 and 10 h on moist paper in light) light response 2 6815 1 2 0.00557109 etiolated 1 4697 1 1 0.0791 Low light 1 888 1 1 0.0153731 waterlogged 1 2259 1 1 0.0387209 waterlogged 1 2259 1 1 0.0387209

The digital expression profile for TC249366 (SEQ ID NO:243 and 251) is listed in Tables 46-48 herein below. TABLE 46 Expression of TC249366 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value root 26 36059 2.69511 9.6471 2.22045E−15 primary root 26 33886 2.5327 10.2657 0 system

TABLE 47 Expression of TC249366 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value germination 26 74869 5.59584 4.64631 7.54952E−15 young 26 34586 2.58502 10.058 0 seedling

TABLE 48 Expression of TC249366 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 21 21216 1.58572 13.2432 7.77156E−16 CONTROL 8 5966 1 8 1.00075E−08 well watered 0 h water 2 6113 1 2 0.0761554 stress 48 h water 7 6417 1 7  3.8251E−07 stress 5 h water 4 2720 1 4 4.97583E−05 stress 5 h and 48 h, Subtracted library

The digital expression profile for TC249365 (SEQ ID NO:244 and 250) is listed in Tables 49-51 herein below. TABLE 49 Expression of TC249365 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flower 11 89278 11.7349 0.937375 0.649792 seedling + 8 9012 1.18456 6.75357 2.20576E−05 female flower silk 3 1536 1 3 0.001119 leaf 3 35689 4.69104 0.639517 0.859653 mix 19 90046 11.8359 1.60529 0.0168681 root 11 36059 4.73968 2.32083 0.00638112 primary 11 33886 4.45405 2.46966 0.00399824 root system seedling 12 32466 4.26741 2.81201 0.000841861 seedling + 8 9012 1.18456 6.75357 2.20576E−05 female flower shoot 4 16152 2.12306 1.88408 0.162096

TABLE 50 Expression of TC249365 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 11 89278 11.7349 0.937375 0.649792 developed 8 9012 1.18456 6.75357 2.20576E−05 seedling + silking silking 3 2160 1 3 0.00293981 germination 26 74869 9.84095 2.64202 3.92859E−07 developed 9 31271 4.11033 2.1896 0.0196511 seedling developed 8 9012 1.18456 6.75357 2.20576E−05 seedling + silking young 9 34586 4.54606 1.97974 0.034885 seedling mix 19 70970 9.32846 2.03678 0.00110629

TABLE 51 Expression of TC249365 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 7 21216 2.78868 2.51015 0.0204171 CONTROL 1 5966 1 1 0.546304 well watered 0 h water stress 1 6113 1 1 0.555122 48 h water stress 5 h 5 6417 1 5 0.00154268 mix 3 36475 4.79436 0.625736 0.869757 pathogen 3 2260 1 3 0.00333671 Fusarium, 6 h 3 667 1 3 9.9034E−05 post infection salinity 4 3579 1 4 0.00127889 150 mM NaCl 4 3579 1 4 0.00127889 24 h

The digital expression profile for AF057183 (SEQ ID NO:245 and 249) is listed in Tables 52-54 herein below. TABLE 52 Expression of AF057183 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flower 15 83646 25.2528 0.593995 0.994869 pollen 1 11265 3.40091 0.294039 0.968401 seedling + 9 8119 2.45113 3.67178 0.000831679 female flower silk 5 1651 1 5 0.000156853 leaf 3 34159 10.3126 0.290906 0.998479 mix 31 88820 26.8148 1.15608 0.205053 root 46 35521 10.7238 4.28952 3.55271E−15 primary 46 33407 10.0856 4.56097 4.88498E−15 root system seedling 13 29180 8.80945 1.47569 0.10175 seedling + 9 8119 2.45113 3.67178 0.000831679 female flower shoot 4 14803 4.46903 0.895049 0.65764

TABLE 53 Expression of AF057183 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 15 83646 25.2528 0.593995 0.994869 developed 9 8119 2.45113 3.67178 0.000831679 seedling + silking silking 5 2284 1 5 0.000684783 tasseling 1 17200 5.19269 0.192579 0.995102 germination 62 70016 21.1379 2.93313 0 developed 13 28013 8.45713 1.53716 0.0800076 seedling developed 9 8119 2.45113 3.67178 0.000831679 seedling + silking young 40 33884 10.2296 3.91023 1.82077E−14 seedling mix 30 66869 20.1878 1.48605 0.0138371

TABLE 54 Expression of AF057183 under various treatments ESTs ESTs in Ex- in Pro- pected Keyword Gene duction ESTs Fold p-value drought 33 21241 6.41266 5.14607 1.42109E−14 CONTROL well 11 5813 1.75495 6.268 1.69797E−06 watered 0 h water stress 48 h 3 6130 1.85065 1.62105 0.282624 water stress 5 h 13 6304 1.90318 6.83067  6.879E−08 water stress 5 h 6 2825 1 6 0.000233093 and 48 h, Subtracted library mix 6 30831 9.30789 0.644614 0.91149 pathogen 5 2415 1 5 0.000877511 Fusarium, 6 h 4 710 1 4 7.00937E−05 post infection Fusarium, 72 h 1 251 1 1 0.0730116 post infection salinity 8 3603 1.08775 7.35465 1.52409E−05 150 mM NaCl 8 3603 1.08775 7.35465 1.52409E−05 24 h

The digital expression profile for TC263205 (SEQ ID NO:246 and 252) is listed in Tables 55-57 herein below. TABLE 55 Expression of TC263205 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flower 1 89278 2.53106 0.395092 0.943664 seedling + female 1 9012 1 1 0.227799 flower mix 3 90046 2.55283 1.17517 0.488081 root 3 36059 1.02228 2.93461 0.075106 primary root 3 33886 1 3 0.0645285 system seedling 1 32466 1 1 0.617579 seedling + female 1 9012 1 1 0.227799 flower

TABLE 56 Expression of TC263205 during development ESTs Ex- in ESTs in pected Keyword Gene Production ESTs Fold p-value flowering 1 89278 2.53106 0.395092 flowering developed 1 9012 1 1 developed seedling + silking seedling + silking germination 4 74869 2.12256 1.88452 germination developed 1 9012 1 1 developed seedling + silking seedling + silking young 3 34586 1 3 young seedling seedling mix 3 70970 2.01202 1.49104 mix Table 56 continued

TABLE 57 Expression of TC263205 under various treatments ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value drought 3 21216 1 3 0.0193621 water stress 5 h 1 6417 1 1 0.167604 water stress 5 h 2 2720 1 2 0.00259071 and 48 h, Subtracted library

The digital expression profile for TC103772 (SEQ ID NO:98) is listed in Tables 58-60 herein below. TABLE 58 Expression of TC103772 in different anatomical regions of the plant ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value leaf 2 17487 1.24628 1.60478 0.358705 seedling 10 95402 6.79917 1.47077 0.053411 leaf 2 19738 1.4067 1.42177 0.419124 leaf + root 2 9479 1 2 0.143927 root 2 7258 1 2 0.092071

TABLE 59 Expression of TC103772 during development ESTs in ESTs in Expected Keyword Gene Production ESTs Fold p-value flowering 2 32705 2.33084 0.858059 0.708441 post-flowering 2 5768 1 2 0.0616601 germination 10 104379 7.43895 1.34428 0.106822 1.5 week 5 47911 3.41455 1.46432 0.236642 2 weeks old 5 27953 1.99217 2.50982 0.0357911

TABLE 60 Expression of TC103772 under various treatments ESTs ESTs in Ex- in Pro- pected Keyword Gene duction ESTs Fold p-value drought 2 18855 1.34377 1.48835 0.395639 drought stress after 2 5768 1 2 0.0616601 flowering light response 3 18685 1.33166 2.25284 0.140391 CONTROL for etiolated 3 8022 1 3 0.0172009 nutrient deficiencies 1 9927 1 1 0.517716 Iron deficient 1 3353 1 1 0.214459 oxidative stress 2 9479 1 2 0.143927 3 12 and 27 h with 2 9479 1 2 0.143927 hydrogen peroxide and Paraquat pathogen 2 17272 1.23095 1.62476 0.352853 Resistant plants, 48 h 2 9051 1 2 0.133444 after Colletotrichum graminicola innoculation (fungi) soil acidity 2 7258 1 2 0.092071 acid and alkaline stress 2 7258 1 2 0.092071 Table 60 continued

Selected polynucleotide sequences (SEQ ID NOs: 93-98) were analyzed for presence of ORFs using Vector NTI suite (InforMax, U.K.) version 6 (Hasting Software, Inc: www.generunner.com/). ORFs identified in each of these polynucleotide sequences were compared to Genbank database sequences, using Blast (www.ncbi.nlm.nih.gov/BLAST/); the ORF displaying the highest homology to a GenBank sequence or sequences, was mapped in order to identify an ATG start codon. The position of the ATG start codon of this ORF was then compared with that of the identified polynucleotide sequence in order to verify that each of the five sequences described herein includes a full length ORF and an ATG start codon (thus qualifies as a “putative monocot ABST gene”).

Polypeptides with significant homology to monocot ABST genes (SEQ ID NOs: 93-98) have been identified from the NCBI databases using BLAST software (Table 61). TABLE 61 ABST homologs ABST Polypeptide Monocot Homologue, ABST Homology in ABST encoded by Polypeptide Polypeptide Putative Gene TIGR Acession Homologue sequence SEQ ID NO. No Source Organism SEQ ID NO: (%) 93 TC270110 Zea mays 105 100 93 TC56855 Saccharum officinarum 106 100 93 TC104838 sorghum 107 100 93 TC57929 Saccharum officinarum 108 98 93 TC103857 sorghum 109 98 93 TC262554 Oryza sativa 110 98 93 TC258871 Zea mays 111 97 93 TC139195 Hordeum vulgare 112 96 93 TC262556 Oryza sativa 113 95 93 TC232174 Triticum aestivum 114 95 93 TC232139 Triticum aestivum 115 95 93 TC139194 Hordeum vulgare 116 95 93 CA486561 Triticum aestivum 117 100 93 TC258873 Zea mays 118 100 93 CA187014 Saccharum officinarum 119 90 93 TC233455 Triticum aestivum 120 96 93 CF063450 Zea mays 121 98 93 CA617041 Triticum aestivum 122 100 94 TC94284 sorghum 123 100 94 TC49791 Saccharum officinarum 124 95 95 TC93449 sorghum 125 100 95 TC49718 Saccharum officinarum 126 95 95 TC49720 Saccharum officinarum 127 96 96 TC92953 sorghum 128 100 96 TC66617 Saccharum officinarum 129 90 96 TC273860 Zea mays 130 91 96 TC253191 Zea mays 131 90 98 TC103772 sorghum 132 100 98 TC272084 Zea mays 133 92 98 TC60928 Saccharum officinarum 134 94 93 TC5422 canola 135 88 93 TC904 canola 136 88 93 TC121774 Solanum tuberosum 137 88 93 TC40342 Gossypium 138 88 93 TC40115 Gossypium 139 88 93 TC155918 Lycopersicon 140 88 esculentum 93 TC154398 Lycopersicon 141 88 esculentum 93 TC154397 Lycopersicon 142 88 esculentum 93 TC153989 Lycopersicon 143 88 esculentum 93 TC120511 Solanum tuberosum 144 88 93 TC113582 Solanum tuberosum 145 88 93 TC112701 Solanum tuberosum 146 88 93 TC111912 Solanum tuberosum 147 88 93 TC4674 Capsicum annum 148 88 93 TC270923 arabidopsis *149 87 93 CD823817 canola 150 86 93 TC526 canola 151 86 93 TC525 canola 152 86 93 BG442528 Gossypium 153 87 93 TC33702 Gossypium 154 87 93 TC32714 Gossypium 155 87 93 TC270782 arabidopsis **156 87 93 TC225449 Glycine max ***157 87 93 TC5255 Capsicum annum 158 88 93 TC28221 populus 159 84 93 TC108140 medicago 160 85 93 TC28222 populus 161 84 93 TC94402 medicago 162 84 93 TC28223 populus 163 83 93 TC102506 medicago 164 85 93 TC132070 Hordeum vulgare 165 79 93 TC251944 Triticum aestivum 166 77 93 NP890576 Oryza sativa 167 76 93 TC280376 Oryza sativa 168 73 93 CN009841 Triticum aestivum 169 75 93 BI948270 Hordeum vulgare 170 75 93 TC259334 arabidopsis 171 75 93 BQ767154 Hordeum vulgare 172 73 93 TC60345 Saccharum officinarum 173 73 93 TC138474 Hordeum vulgare 174 85 93 TC41472 populus 175 72 93 BJ458177 Hordeum vulgare 176 72 93 CB674176 Oryza sativa 177 82 93 TC216405 Glycine max 178 88 93 AJ777371 populus 179 70 93 CV019213 tobacco 180 85 93 CK215690 Triticum aestivum 181 80 93 CD830784 canola 182 85 93 CA624722 Triticum aestivum 183 85 93 TC32906 populus 184 76 93 CR285127 Oryza sativa 185 89 93 TC251945 Triticum aestivum 186 72 94 TC274823 Oryza sativa 187 77 94 TC132394 Hordeum vulgare 188 75 94 TC267180 Triticum aestivum 189 77 94 TC261921 Zea mays 190 87 94 TC267181 Triticum aestivum 191 74 94 TC261922 Zea mays 192 81 94 TC267182 Triticum aestivum 193 73 95 TC249531 Zea mays 194 86 95 TC232170 Triticum aestivum 195 85 95 TC146720 Hordeum vulgare 196 85 95 TC249329 Oryza sativa 197 84 95 TC249532 Zea mays 198 88 95 TC232150 Triticum aestivum 199 85 95 TC249330 Oryza sativa 200 76 95 CB672603 Oryza sativa 201 71 95 TC32440 Gossypium 202 81 95 TC119105 Solanum tuberosum 203 72 96 TC247999 Triticum aestivum 204 78 96 TC247359 Triticum aestivum 205 77 96 TC132566 Hordeum vulgare 206 77 96 TC248676 Triticum aestivum 207 74 96 TC249667 Oryza sativa 208 77 96 TC66618 Saccharum officinarum 209 88 97 TC253495 Oryza sativa 214 90 97 TC224823 Glycine max 215 75 97 TC234990 Triticum aestivum 216 74 97 TC266178 Triticum aestivum 217 73 97 TC119051 Solanum tuberosum 218 83 97 TC56409 Saccharum officinarum 219 75 97 TC35873 Populus 220 80 97 TC119052 Solanum tuberosum 221 82 97 TC204518 Glycine max 222 85 97 TC112169 Solanum tuberosum 223 84 97 TC254696 Zea mays 224 79 97 TC254696 Zea mays 225 82 97 TC248906 Oryza sativa 226 77 97 TC154007 Lycopersicon 227 82 esculentum 97 TC6466 Capsicum annuum 228 74 97 TC131227 Hordeum vulgare 229 74 97 TC27564 Gossypium 230 71 98 TC275473 Oryza sativa 210 78 98 TC267485 Triticum aestivum 211 77 98 TC148621 Hordeum vulgare 212 76 98 TC275474 Oryza sativa 213 85 *SEQ ID NO: 149 is identical to SEQ ID NO: 41 **SEQ ID NO: 156 is identical to SEQ ID NO: 42 ***SEQ ID NO: 157 is identical to SEQ ID NO: 40

Example 12 Generating Putative Monocot ABST Genes

A sequences of six putative Monocot ABST genes were synthesized by GeneArt (http://vww.geneart.com/). Synthetic DNA was designed in silico, based on the encoded amino-acid sequences of the Monocot ABST genes (SEQ ID NOs: 99, 100, 101, 102, 103 and 104), and by using plant-based codon-usage. The synthetic sequences and the plant native orthologues were compared. At least 1 mutation per 20 nucleotide base pairs was added to avoid possible silencing, when over-expressing the gene in favorable monocot species, such as maize. The planned sequences were bordered with the following restriction enzymes sites polylinker—SalI, XbaI, BamHI, SmaI at the 5′ end and SacI at the 3′ end. The sequences were cloned in double strand, PCR Script plasmid (GeneArt).

Example 13 Cloning the Putative ABST Genes

The PCR Script plasmids harboring the synthetic, monocot-based ABST genes were digested with the restriction endonucleases XbaI and SacI (Roche), purified using PCR Purification Kit (Qiagen, Germany), and inserted via DNA ligation using T4 DNA ligase enzyme (Roche) and according to the manufacturer's instructions, into pKG(NOSter), (SEQ ID NO: 233) and pKG(³⁵S+NOSter), (SEQ ID NO: 234), plant expression vector plasmids, also digested with XbaI and SacI (Roche) and purified pKG plasmid is based on the PCR Script backbone (GeneArt), with several changes in the polylinker site to facilitate cloning a gene of interest downstream to a promoter and upstream to a terminator, suitable for expression in plant cells. Moreover, the inserted gene, together with the promoter and the terminator could be easily moved to a binary vector.

The resulting pKG(NOSter) and pKG(35S+NOSter) harboring putative Monocot ABST genes were introduced into E. coli DH5 competent cells by electroporation, using a MicroPulser electroporator (Biorad), 0.2 cm cuvettes (Biorad) and EC-2 electroporation program (Biorad). The treated cells were cultured in LB liquid medium at 37° C. for 1 hour, plated over LB agar supplemented with ampicillin (100 mg/L; Duchefa) and incubated at 37° C. for 16 hrs. Colonies that developed on the selective medium were analyzed by PCR using the primers of SEQ ID NO: 231 and SEQ ID NO: 232, which were designed to span the inserted sequence in the pKG plasmids. The resulting PCR products were separated on 1% agarose gels and from the colonies having the DNA fragment of the predicted size, a plasmid was isolated using miniprep Plasmid Kit (Qiagen) and sequenced using the ABI 377 sequencer (Amersham Biosciences Inc) in order to verify that the correct DNA sequences were properly introduced to the E. coli cells.

Positive pKG(NOSter) plasmids harboring putative Monocot ABST genes were digested with the restriction enzymes HindIII and SalI (Roche), purified using PCR Purification Kit (Qiagen, Germany), and then ligated (as described above) with At6669 promoter sequence (set forth in SEQ ID NO: 20) digested from pPI+At6669 plasmid with the same enzymes and purified. The resulting plasmids were introduced into E. coli DH5 competent cells by electroporation, the treated cells were cultured in LB liquid medium at 37° C. for 1 hr, subsequently plated over LB agar supplemented with ampicillin (100 mg/L; Duchefa) and incubated at 37° C. for 16 hours. Colonies grown on the selective medium were analyzed by PCR using the primers SEQ ID NO: 235 and SEQ ID NO: 232. Positive plasmids were identified isolated and sequenced as described above.

The plasmid pPI was constructed by inserting a synthetic poly-(A) signal sequence, originating from pGL3 basic plasmid vector (Promega, Acc No U47295; bp 4658-4811) into the HindIII restriction site of the binary vector pBI101.3 (Clontech, Acc. No. U12640).

The At6669 promoter was isolated from Arabidopsis thaliana var Col0 genomic DNA by PCR amplification using the primers set forth in SEQ ID NOs: 37 and 38. The PCR product is purified (Qiagen, Germany) and digested with the restriction endonucleases HindIII and SalI (Roche). The resulting promoter sequence was introduced into the open binary pPI vector digested with the same enzymes, to produce pPI+At6669 plasmid.

Example 14 Generating Binary Vectors Comprising Putative Monocot ABST Genes and Plant Promoters Operably Linked Thereto

Generating binary vectors comprising the Cauliflower Mosaic Virus 35S promoter: The five pKG(35S+NOSter) constructs harboring putative Monocot ABST genes (SEQ ID Nos: 93, 94, 95, 96, 97 and 98) were digested with HindIII and EcoRI (Roche) restriction endonucleases in order to excise expression cassettes and ligated to pPI plasmid digested with the same endonucleases and purified (as described above). Altogether, five pPI constructs wer generated, each comprising putative Monocot ABST gene having a sequence set forth in SEQ ID NOs: 93, 94, 95, 96, 97 and 98 positioned downstream to the Cauliflower Mosaic Virus 35S promoter and upstream to the Nopaline Synthase (NOS) terminator, which was originated from the digestion of pBI101.3 (Clontech, Acc. No. U12640), using the restriction sites SacI and EcoRI.

Generating binary vectors comprising the At6669 promoter: The five pKG(At6669+NOSter) constructs harboring putative Monocot ABST genes downstream to At6669 promoter sequence (set forth in SEQ ID NO: 20), and upstream to the Nopaline Synthase (NOS) terminator, were digested with HindIII and EcoRI (Roche) in order to excise expression cassettes and ligated into pPI plasmid which was digested with the same restriction endonucleases and purified (as described above). Altogether, five pPI constructs were generated, each comprising the At6669 promoter positioned upstream of a putative Monocot ABST gene having a sequence set forth in SEQ ID NOs: 93, 94, 95, 96, 97 and 98.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents, patent applications and sequences identified by their accession numbers mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application or sequence identified by their accession number was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

REFERENCES CITED Additional References are Cited Hereinabove

-   1. www.fao.org/ag/agl/agll/spush/degrad.htm. -   2. www.fao.org/ag/agl/aglw/watermanagement/introduc.stm -   3. McCue K F, Hanson A D (1990). Drought and salt tolerance: towards     understanding and application. Trends Biotechnol 8: 358-362. -   4. Flowers T J, Yeo Ar (1995). Breeding for salinity resistance in     crop plants: where next? Aust J Plant Physiol 22:875-884. -   5. Nguyen B D, Brar D S, Bui B C, Nguyen T V, Pham L N, Nguyen H T     (2003). Identification and mapping of the QTL for aluminum tolerance     introgressed from the new source, ORYZA RUFIPOGON Griff., into     indica rice (Oryza sativa L.). Theor Appl Genet. 106:583-93. -   6. Sanchez A C, Subudhi P K, Rosenow D T, Nguyen H T (2002). Mapping     QTLs associated with drought resistance in sorghum (Sorghum     bicolor L. Moench). Plant Mol Biol. 48:713-26. -   7. Quesada V, Garcia-Martinez S, Piqueras P, Ponce M R, Micol J L     (2002). Genetic architecture of NaCl tolerance in Arabidopsis. Plant     Physiol. 130:951-963. -   8. Apse M P, Blumwald E (2002). Engineering salt tolerance in     plants. Curr Opin Biotechnol. 13:146-150. -   9. Rontein D, Basset G, Hanson A D (2002). Metabolic engineering of     osmoprotectant accumulation in plants. Metab Eng 4:49-56 -   10. Clough S J, Bent A F (1998). Floral dip: a simplified method for     Agrobacterium-mediated transformation of Arabidopsis thaliana. Plant     J 16:735-43. -   11. Desfeux C, Clough S J, Bent A F (2000). Female reproductive     tissues are the primary target of Agrobacterium-mediated     transformation by the Arabidopsis floral-dip method. Plant Physiol     123:895-904. 

1. A method of increasing tolerance of a plant to an abiotic stress, comprising expressing within the plant an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252, thereby increasing the tolerance of the plant to the abiotic stress.
 2. The method of claim 1, wherein said expressing is effected by: (a) transforming a cell of said plant with said exogenous polynucleotide; (b) generating a mature plant from said cell; and (c) cultivating said mature plant under conditions suitable for expressing said exogenous polynucleotide within said mature plant.
 3. The method of claim 2, wherein said transforming is effected by introducing to said plant cell a nucleic acid construct including said exogenous polynucleotide and at least one promoter capable of directing transcription of said exogenous polynucleotide in said plant cell.
 4. The method of claim 3, wherein said at least one promoter is a constitutive promoter.
 5. The method of claim 3, wherein said constitutive promoter is CaMV 35S promoter.
 6. The method of claim 3, wherein said constitutive promoter is At6669 promoter.
 7. The method of claim 3, wherein said at least one promoter is an inducible promoter.
 8. The method of claim 7, wherein said inducible promoter is an abiotic stress inducible promoter.
 9. The method of claim 1, wherein said expressing is effected by infecting said plant with a virus including said exogenous polynucleotide.
 10. The method of claim 9, wherein said virus is an avirulent virus.
 11. The method of claim 1, wherein said abiotic stress is selected from the group consisting of salinity, water deprivation, low temperature, high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, nutrient excess, atmospheric pollution and UV irradiation.
 12. The method of claim 1, wherein said plant is a dicotyledonous plant.
 13. The method of claim 1, wherein said plant is a monocotyledonous plant.
 14. A method of increasing biomass and/or yield of a plant, comprising expressing within the plant an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18, 93-98 and 247-252, thereby increasing biomass of the plant.
 15. The method of claim 14, wherein said expressing is effected by: (a) transforming a cell of said plant with said exogenous polynucleotide; (b) generating a mature plant from said cell; and (c) cultivating said mature plant under conditions suitable for expressing said exogenous polynucleotide within said mature plant.
 16. The method of claim 15, wherein said transforming is effected by introducing to said plant cell a nucleic acid construct including said exogenous polynucleotide and at least one promoter capable of directing transcription of said exogenous polynucleotide in said plant cell.
 17. The method of claim 16, wherein said at least one promoter is a constitutive promoter.
 18. The method of claim 17, wherein said constitutive promoter is CaMV 35S promoter.
 19. The method of claim 17, wherein said constitutive promoter is At6669 promoter.
 20. The method of claim 16, wherein said at least one promoter is an inducible promoter.
 21. The method of claim 14, wherein said expressing is effected by infecting said plant with a virus including said exogenous polynucleotide.
 22. The method of claim 21, wherein said virus is an avirulent virus.
 23. The method of claim 14, wherein said plant is a dicotyledonous plant.
 24. The method of claim 14, wherein said plant is a monocotyledonous.
 25. A nucleic acid construct, comprising a polynucleotide at least 90% homologous to a nucleotide sequence selected from the group consisting of SEQ ID NOs: 1-18 and 93-98 and 247-252 and a promoter capable of directing transcription of the polynucleotide in a host cell.
 26. The nucleic acid construct of claim 25, wherein said promoter is a constitutive promoter.
 27. The nucleic acid construct of claim 26, wherein said constitutive promoter is CaMV 35S promoter.
 28. The nucleic acid construct of claim 26, wherein said constitutive promoter is At6669 promoter.
 29. The nucleic acid construct of claim 25, wherein said promoter is an inducible promoter.
 30. The nucleic acid construct of claim 29, wherein said inducible promoter is an abiotic stress inducible promoter.
 31. The nucleic acid construct of claim 25, wherein said host cell is a plant cell.
 32. The nucleic acid construct of claim 31, wherein said plant cell forms a part of a dicotyledonous plant cell.
 33. The nucleic acid construct of claim 31, wherein said plant cell forms a part of a monocotyledonous plant cell.
 34. An isolated polypeptide, comprising an amino acid sequence at least 90% homologous to the amino acid sequence encoded by a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18 and 93-98 and 247-252.
 35. A plant cell comprising an exogenous polynucleotide at least 90% homologous to a polynucleotide selected from the group consisting of SEQ ID NOs: 1-18 and 93-98 and 247-252.
 36. The plant cell of claim 35, wherein said plant cell forms a part of a plant. 